Sticker Groups Research Articles

Free energy calculations in associative polymers using molecular dynamics

ABSTRACT In this work, equilibrium molecular dynamics is used to predict the change in the Helmholtz free energy () for solutions of associative polymers of the telechelic type. is calculated using the thermodynamic integration method, wherein molecular chains are simulated in a coarse-grain scale within an NVT ensemble. Simulations take place in the concentration interval , such that aggregate formation is possible. The initial configuration is that of dispersed free chains; the increase of interactions among stickers signals the onset of the micelle formation process. The solution with high concentration experiences substantial micelle aggregation despite little conformation changes. Therein, transient networks among micellar flowers are formed. The decrease in free energy is related to the formation of aggregates to achieve stability. When solutions are thermodynamically stable, the free energy and configurational entropy decrease and increase non-linearly with concentration, respectively. Below critical micellar concentration, this behaviour is associated with a step-by-step process along which the sticker groups gather to form the first thermodynamically stable aggregate. Above critical micellar concentration, the most probable distribution increases with concentration, therefore, free energy decreases with increasing aggregates that form the network.

Application value of a new lesion positioning stickers in breast lesion surface localization.

Accurate breast lesion surface localization can guarantee accurate biopsy and local treatment. But there is no guideline to regular equipment and methods for the localization of breast lesions. The conventional non-invasive localization method is marker-based localization. The advantages of this method are simple and efficient. The disadvantages are that markers disappear easily under coupling agents; the positioning length of markers cannot last long on skin; and healthcare associated infection due to many patients using the same marker pen is potentially unavoidable. Breast lesion sticker (called sticker for short) is a new-type localization medical instrument in 2020. Our study aims to explore the clinical value of a new lesion stickers in breast lesion surface localization via comparison of the sticker and marker pen localization methods. This was a prospective cohort study. It was conducted in 67 patients who needed breast lesion surface localization before biopsy. The patients were randomly assigned into 2 groups. One group of patients used marker pen to mark breast lesion surface location by ultrasonography. The other group of patients used stickers. Patients labeled with markers on skin were swabbed agents before marking. Then the markers were checked by ultrasound scan. If the surface positions of breast lesion were not correct, the above procedure was repeated. In the sticker group, the stickers were released synchronously after the lesions were detected by ultrasound scan. Then locations were checked via scanning hole. If the surface positions of breast lesion were not correct, the above procedure was repeated. The accuracy of positioning, the length of positioning time and satisfaction of patients between the 2 groups were compared. The length of positioning time was calculated from the time when ultrasound detected the lesion to the time when the surface position of breast lesion was confirmed. The total score of patients' satisfaction was 5 points according to Service Quality Evaluation of SERVQUAL Scale, including sonographers' service attitude and their technical proficiency, other medical staffs' service attitude and their technical proficiency, hospital service procedures, positioning comfort, and positioning effects. All 67 patients were females, aged 18-66 (39.73±13.10). There were 35 patients in the marker pen group and 32 patients in the sticker group. The time length of group used marker pen to localization was 22-88 (52.20±2.90) s, and the sticker group was 3-15 (9.22±0.58) s in length. The length of positioning time for the stickers was significantly shorter than that of the marker (P<0.01). Both methods were accurate in the surface localization of lesions before operation. The total scores of patients' satisfaction was 4-5 (4.92±0.02) in the stickers group, and 1-5 (3.35±0.10) in the marker pen group. The patients' satisfaction scores with the sticker were significantly higher than those with the marker pen (P<0.01). The length of positioning time and patients' satisfication scores for sonographer with 20 years' working experience were shorter and higher than those of sonographer with 10 years' working experience, respectively (both P<0.05). The new breast lesion positioning stickers have more advantages than the marker pen in localization efficiency. It could reduce the workload of medical workers and increase patients' satisfaction to some extent. The stickers can be used not only in the breast lesions surface localization, but also in the skin location of pleural effusion and ascites, the skin location of surface masses, the skin location of thyroid nodule, and many other clinical marker areas, to further expand the scope of clinical application and value of the stickers.

Molecular dynamics of shear banding flow in associative polymers solutions: effect of sticker groups location

Non-equilibrium molecular dynamics are used in a coarse-grained scale to simulate the simple shear flow of telechelic and non-telechelic associative polymer solutions. The work includes the study of inception of flow and stress relaxation in transient flows and the constitutive curve at steady state. The instabilities (plateau stress, stress maxima) and the formation of bands with different velocity gradient and concentration depend on the location of the hydrophobic sites (sticker sites, SS) in the chain. Results allow to shed light on the origin of banded flow within the transient state, related to depletion of bridges between aggregates. This situation induces instabilities in the velocity profiles and concentration inhomogeneities along the velocity gradient during the stress overshoot. As the steady state is reached, instabilities disappear for systems where the SS are in the middle of the chain. The conformation relaxation occurs during a time scale larger than that of the stress, but this is not sufficient condition for the presence of banded flow in telechelic polymer solutions, as it holds in polymer melts. The difference in concentration among the bands suggests the existence of a shear-gradient concentration coupling mechanism under banded flow conditions, such as spatial non-homogeneities in the network density, induces chain diffusivity in the gradient direction and increasing normal stresses, especially in telechelic chains. The role of normal stresses on the flow-concentration coupling instability is analyzed in detail.

Physical Bond Breaking in Associating Copolymer Liquids.

We combine ideas from polymer and glassy liquid physics to construct a new model for the bond-breaking time scale of attractive sticker groups in associating copolymer liquids that form transient networks. The activated event is argued to be a two-step process, involving first the release of the nonsticker dynamic caging constraints that defines the primary alpha relaxation, followed by attractive stickers surmounting an association free-energy barrier subject to a local frictional resistance which can be strongly affected by relaxation-diffusion decoupling. The ideas embedded in the model produce a consistent and good description of the bond-breaking time scale for diverse polymer chemistries and architectures as a function of temperature and fraction of sticky groups. Chemically sensible values for association free energies are deduced. In strong contrast, the existing phenomenological models are shown to incur qualitative failures.

Home-based records and vaccination appointment stickers as parental reminders to reduce vaccination dropout in Indonesia: A cluster-randomized controlled trial

IntroductionLimited evidence is available about the effectiveness of strategies to remind caregivers when to bring children back for future vaccinations in low- and middle-income country settings. We evaluated the effectiveness of two reminder strategies based on home-based vaccination records (HBR) in Indonesia. MethodsIn this cluster-randomized controlled trial involving 3616 children <1 year of age, 90 health facilities were randomly assigned to either a control group or one of two intervention groups: (1) HBR-only group, where healthcare workers provided an HBR to any child without an HBR during a vaccination visit and instructed the caregiver to keep it at home between visits, or (2) HBR + sticker group, where, in addition to HBR provision, healthcare workers placed vaccination appointment reminder stickers on the HBR. The primary outcome was receipt of the third dose of diphtheria-tetanus-pertussis-containing vaccine (DTPcv3) within 7 months and the secondary outcome was receipt of a timely DTPcv3 dose. ResultsControl group DTPcv3 coverage was 81%. In intention-to-treat analysis, neither intervention group had significantly different DTPcv3 coverage compared with the control group (RR = 0.94, 95% confidence interval [CI] 0.87; 1.02 for HBR-only group; RR = 0.97, 95% CI 0.90; 1.04 for HBR + sticker group) by study end. However, children in the HBR + sticker group were 50% more likely to have received a DTPcv3 vaccination (RR = 1.46, 95% CI 1.02, 2.09) within 60 days of DTPcv1 vaccination, compared with children in the control group; children in the HBR-only group were not more likely to have done so (RR = 1.05, 95% CI 0.71, 1.55). DiscussionReminder stickers had an immediate effect on coverage by improving the proportion of children who received a timely DTPcv3 dose but no effect on the proportion who received DTPcv3 after 7 months. Coupling reminder stickers with strategies to address other reasons why children do not return for vaccination visits should be further explored.

Supramolecular gels of cholesterol-modified gellan gum with disc-like and worm-like micelles

The association between a hydrophobically modified polysaccharide, gellan gum, with micelles based on a surfactant bearing the same hydrophobic tail as pendant groups was investigated by rheology and small-angle neutron scattering (SANS). Gellan gum grafted with cholesterol groups (20% mol/mol tetrasaccharide unit), GeCh, was mixed with polyoxyethylene cholesteryl ether (ChEO10), which comprises a cholesterol group as the tail linked to a small polyoxyethylene headgroup, and self-assembles into micelles with an unusual disc-like morphology. The addition of 0.5% polymer to solutions of ChEO10 induced a remarkable transition from a Newtonian fluid to a predominantly solid-like viscoelastic behaviour, leading to a ×105 increase in zero-shear viscosity (with 5% ChEO10). Increasing surfactant concentration led to an enhancement of the viscoelasticity, but the elastic modulus G′ reached a plateau around 15% surfactant, attributed to a saturation of the sticker groups. The effect of micellar morphology on the network was studied by adding a small headgroup co-surfactant, triethylene glycol monododecyl ether, to ChEO10 micelles, which drives their elongation into wormlike micelles. Networks obtained with the long, flexible micelles displayed enhanced solid-like behaviour, with no cross-over between G′ and G″ over the measured range of frequencies, reflecting relaxation times of the order of minutes or hours. The morphology of the gels studied by SANS revealed a scattering dominated by strongly interacting micelles (described by discs of 140 Å diameter and a hydrated ∼38 Å PEO corona) and the presence of micellar clusters induced by the presence of the polymer. The scattering data therefore confirm that the onset of gelation is due to surfactant micelles acting as junction points for the network.

Physical Networks from Multifunctional Telechelic Star Polymers: A Rheological Study by Experiments and Simulations.

The equilibrium mechanical properties of a cross-linked gel of telechelic star polymers are studied by rheology and Brownian dynamics simulations. The Brownian dynamics model consists of cores to which Rouse arms are attached. Forces between the cores are obtained from a potential of mean force model developed by Likos and co-workers. Both experimentally and in the simulations, networks were created by attaching sticker groups to the ends of the arms of the polymers, which were next allowed to form bonds among them in a one to one fashion. Simulations were sped up by solving the Rouse dynamics exactly. Moreover, the Rouse model was extended to allow for different frictions on different beads. In order to describe the rheology of the non-cross-linked polymers, it had to be assumed that bead frictions increase with increasing bead number along the arms. This friction model could be transferred to describe the rheology of the network without any adjustments other than an overall increase of the frictions due to the formation of bonds. The slowing down at intermediate times of the network rheology compared to that of the non-cross-linked polymers is well described by the model. The percentage of stickers involved in forming inter-star bonds in the system was determined to be 25%, both from simulations and from an application of the Green–Tobolsky relation to the experimental plateau value of the shear relaxation modulus. Simulations with increasing cross-link percentages revealed that on approaching the gel transition the shear relaxation modulus develops an algebraic tail, which gets frozen at a percentage of maximum cross-linking of about 11%.

Effect of Neutralization on the Structure and Dynamics of Model Ionomer Melts

Using coarse-grained molecular dynamics simulations, we investigate how ionomer behavior depends on ion and acid content. Our coarse-grained model builds on a prior model that was successful in capturing the low wavevector ionomer peak observed in X-ray scattering. As in prior work, we consider a linear backbone of neutral monomer beads with charged pendant beads and unbound counterions; we now also include “stickers” pendant to the backbone to represent unneutralized acid groups. These stickers are similar to backbone monomers but have higher cohesive interaction strength with each other and with the ionic groups, chosen to approximately match structural features of prior atomistic simulations. This allows us to simulate partially neutralized materials over longer time and length scales than is possible atomistically. We find that stickers can aid in ionic aggregate rearrangements such that samples containing sticker groups can show a lower viscosity than samples with the same ion content but without sti...

Probing hydrogen bond interactions in a shear thickening polysaccharide using nonlinear shear and extensional rheology

Mamaku gum is a polysaccharide extracted from the fronds of the black tree fern found in New Zealand. The cooked pith has traditionally been used for various medicinal purposes and as a food source by the Ma¯ori people of New Zealand. It has potential applications as a thickener in the food industry and as a palliative for patients with dysphagia. Studies on the shear rheology of Mamaku gum have revealed that the gum exhibits shear thickening at a critical shear rate due to a transition from intra- to inter-molecular chain interactions upon shear-induced chain elongation. In this paper, we demonstrate that these interactions are primarily due to hydrogen bonding. We perform extensional rheology on mixtures of Mamaku gum and urea (a known disruptor of hydrogen bonds) to quantify the nature of these interactions. Capillary Breakup Extensional Rheometry (CaBER) performed on the pure Mamaku gum solutions yield plateau values of the Trouton ratio as high as ∼104, showing that the viscoelasticity of the gum in uniaxial elongation is much higher than in shear. For all Mamaku concentrations tested, the extensional viscosity decreases upon increasing urea concentration. Furthermore, the relaxation time decreases exponentially with increasing urea concentration. This exponential relationship is independent of the Mamaku concentration, and is identical to the relationships between urea concentration and characteristic timescales measured in nonlinear shear rheology. We show using the sticky reptation model for polymers with multiple sticker groups along the backbone how such a relationship is consistent with a linear decrease in the free energy for hydrogen bond dissociation. We then demonstrate that a time-concentration superposition principle can be used to collapse the viscoelastic properties of the Mamaku-gum/urea mixtures.

Linear rheology of bis-urea functionalized supramolecular poly(butylacrylate)s: Part I – weak stickers

We investigated the linear viscoelastic properties in the melt of a series of nearly monodisperse poly(n-butyl acrylate) (PnBA) chains center-functionalized with a bis-urea sticker group, able to self-associate by quadruple hydrogen bonding. All materials are viscoelastic liquids at 40 °C and their Newtonian viscosity varies from 100 to 5000 Pa s. However we show clearly that the viscosity changes non monotonously going through a minimum for a molecular weight (Mn) of 20 kg/mol and a sticker density of 1.1 wt%. We found two regimes: For Mn < 20 kg/mol, the viscosity increases with decreasing Mn, the linear viscoelastic properties change dramatically with temperature, forming a viscoelastic gel at 0 °C and flowing at 40 °C and the strength of the stickers association controls the size of molecular aggregates. However for Mn > 20 kg/mol, the viscosity increases with Mn, the rheology is controlled by the polymer dynamics and the stickers simply increase the terminal relaxation time relative to unfunctionalized PnBA of the same Mn, as expected from sticky reptation theory. Despite clear evidence of sticker–sticker interactions by FTIR, none of the materials self-assemble at 20 °C into structures with a long range order detectable by SAXS.

Quantitative mesoscale modeling of the oscillatory and transient shear rheology and the extensional rheology of pressure sensitive adhesives

The development of novel pressure sensitive adhesives, formed by the drying of a polymer latex emulsion, is hampered by a lack of understanding of the relation between microscopic details and the large-scale rheology. In a previous paper [Soft Matter, 2011, 7, 5036] we introduced a coarse-grained computer simulation model that aims to provide such a link. To reach sufficiently large time and length scales each latex particle is represented by just six degrees of freedom, and transient forces are introduced to capture the effect of slow changes in the degree of chain intermixing and in the number of sticker groups shared between pairs of latex particles. In this paper we show that this model can nearly quantitatively predict the shear and extensional nonlinear rheology by careful tuning of only a few parameters to the linear rheology. We find a complex transient viscosity with multiple inflection points and maxima under shear flow, as well as a strong strain hardening under extensional flow, all in agreement with experimental observations. We investigate the influence of each of the model's parameters on the linear and nonlinear rheology.

Polymer-Solid Interface Connectivity and Adhesion: Design of a Bio-Based Pressure Sensitive Adhesive

Adhesion at polymer-solid interfaces was explored for a new bio-based pressure sensitive adhesive (PSA) in terms of sticker groups, φX, on the polymer phase, receptor groups, φY, on the solid surface, and the bond strength of the sticker-receptor X-Y acid-base interaction, χ. The polymer-solid interface restructuring models of Gong and Lee et al. were extended with new percolation models of entanglements and interface strength to determine the optimal sticker group concentration, φ*X. For the general case where φY and χ are constant, it is predicted that when φX < φ*X, that the critical peel energy behaves as G1c ∼ φX/φ*X and the locus of failure is adhesive between the polymer and the solid. However, when φX > φ*X, failure occurs cohesively in a polymer-polymer interface adjacent to the solid and the strength decreases as G1c ∼ φ*X/φX. The switch from adhesive to cohesive failure can be understood in terms of the changes in the chain conformations of the adhered chains and their decreasing interpenetration, Xi, with the bulk chains, via Xi ∼ 1/r, where r = χφXφY. The optimal value of φX which maximizes the adhesion and determines the mode of failure is given by φ*X ≈ 0.129/C∝, and for typical values of the characteristic ratio C∝ in the range 7–20, φ*X ≈ 1% mole fraction, corresponding to about 2 sticker groups per entanglement molecular weight, Me. This result was verified for a bio-based PSA synthesized from an acrylated high oleic fatty acid, which was copolymerized with maleic anhydride as the sticker group. The observed behavior is counterintuitive to the current wisdom for the effect of acid-based interactions on adhesion, where the strength is expected to increase with the number of X-Y contacts. The surprisingly low value of φ*X ≈ 1% sticker groups which maximizes the adhesion strength can now be readily calculated using the percolation model of entanglements and fracture.

Thermodynamic analysis of polymer‐solid adhesion: Sticker and receptor group effects

AbstractAdhesion of dense linear polymer chains containing a small number of randomly distributed sticker groups (ϕX) to a solid substrate containing receptor groups (ϕY) has been analyzed by a single‐chain scaling approach. An entanglement sink probability (ESP) model motivated by vector percolation explains the nonmonotonic influences of sticker concentration (ϕX), receptor concentration (ϕY), and their interaction strength (χ) on the adhesion strength GIC of the polymer‐solid interface. The ESP model quantifies the degree of interdigitation between adsorbed and neighboring chains on the basis of the adsorbed chain domain with an extension of the scaling treatment of de Gennes. Here, the adsorbed chain domain changes thermodynamically with respect to the energy of interaction parameter, r = χϕXϕY. This model considers the situation of a blend consisting of a small volume fraction of adhesive molecules as a compatibilizer at the interface, where these molecules promote adhesion by adsorbing to the surface via sticker‐receptor interactions. The percolation model scales solely with r = χϕXϕY, and this parameter can be related to both the adhesive potential (GA) and the cohesive potential (GC). GA describes adhesive failure between adsorbed chains and the solid surface and linearly behaves as GA ∼ r = χϕXϕY. The cohesive strength between adsorbed and neighboring chains corresponds to GC ∼ r−0.5∼−1.0 = (χϕXϕY)−0.5∼−1.0. When the fracture stresses for cohesive and adhesive failure are equal, the model predicts maximum adhesion strength at an optimal value of r* = (χϕXϕY)*. Thus, for a given χ value, optimal values ϕ and ϕ exist for the sticker and receptor groups, above or below which the fracture energy will not be optimized. Alternatively, if the X‐Y interaction strength χ increases, then the number of sticker groups required to achieve the optimum strength decreases. Significantly, the optimum strength is not obtained when the surface is completely covered with receptor groups (ϕY = 1) but is closer to 30%. For polybutadiene, the optimum value of r* was determined experimentally (Lee, I.; Wool, R. P. J Adhesion 2001, 75, 299), and typically ϕ ≈ 1–3%, ϕ ≈ 25–30%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2343–2353, 2002

Conformation of Adsorbed Random Copolymers: A Solid-State NMR and FTIR-PAS Study

The properties of bulk and adsorbed polyethylene-co-acrylic acid (PEA) random copolymers were characterized by solid-state NMR and vibrational spectroscopy. FTIR-PAS (Fourier transform infrared photoacoustic spectroscopy) measurements show that the copolymers are chemisorbed to zirconia surfaces via the carboxylic acid sticker groups. The chain mobility, conformation, and morphology of bulk and adsorbed PEA were studied by 13C CP-MAS, 2D WISE, and 1H spin diffusion NMR experiments. The effect of the copolymer loading and acrylic acid content on these properties was examined. Whereas adsorbed PEA with a 5% w/w acrylic acid content contain transoid chain segments at all loadings, samples with higher acrylic acid contents (15 % w/w) only display an all-trans component at higher loadings where unbound acid groups are present.

Optimum Polymer - Solid Interface Design for Adhesion Strength: Carboxylation of Polybutadiene and Mixed Silanes Surface Modification of Aluminum Oxide

To understand the optimum design of polymer-solid interfaces for adhesion strength, model polymer-solid interfaces of carboxylated polybutadiene(cPBD) adhered to mixed silane modified Al2O3 surfaces were examined. The cPBD, having various ‒COOH sticker group concentration φ(X) (0 ∼ 10 mol%), was synthesized through high-pressure carboxylation of PBD, while Al2O3 surfaces were modified to have various -NH2 density, φ(Y) (0 ∼ 100 mol%), using self-assembly of mixed amine- and methyl-terminated silanes. The coadsorption kinetic model of the two silanes was analyzed through X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and dynamic contact angle (DCA), which gave the capability of controlling the receptor concentration of aluminum oxide surfaces. The polymer surface chain responses after exposure to various media were understood by measuring contact angle changes of various probe liquids. T-peel tests of the model polymer–solid interfaces, as a function of time and sticker and receptor group concentrations showed much longer time dependence than the characteristic time of a bulk polymer chain. Additionally, the classical equation of interface failure was re-examined to see the effects of deformation rate, annealing temperature, and annealing time. A simple scaling analysis of free energy of an adsorbed polymer on a solid surface was extended to predict the adhesion potential of the model polymer–solid interfaces. From the experiments and theory of adhesive vs. cohesive failure, it was found that there existed an optimum product value r* = φ(X)φ(Y)χ of sticker concentration φ(X), receptor concentration φ(Y), and their interaction strength χ, which was approximately 150 cal/mol for this polymer–solid interface. Below or above this optimum product value r*, the fracture energy of polymer-solid interfaces, G IC, was less than its optimal value, G lc*.

Diffusion of Model Hydrophobic Alkali-Swellable Emulsion Associative Thickeners

Diffusion coefficients of hydrophobically modified alkali-swellable (HASE) associating polymers (APs) in aqueous solution were measured using pulsed gradient spin-echo (PGSE) nuclear magnetic resonance (NMR). HASE APs consist of a copolymer of methacrylic acid and ethyl acrylate to which hydrophobic “sticker groups” are attached through a poly(ethylene oxide) (PEO) “spacer arm”. Two series of HASE APs were investigated: one in which the length of the hydrophobic alkyl chain was varied (CxE35) and another in which the length of the PEO spacer arm was varied (C20Ey). With increasing hydrophobe or PEO spacer arm length the average diffusion coefficient decreased, reflecting the viscosity enhancement produced by the associating network formed by HASE polymers. The effect of external variables such as concentration, pH, and temperature mirrored established rheological properties for such systems. The average diffusion behavior, however, was the result of a superposition of two contributions, one slow (D0 < 1 × 10-11 m2 s-1) and one fast (D0 ≈ 1 × 10-10 m2 s-1) diffusing. Changing the hydrophobe chain length or the PEO spacer arm length modulated the proportion of the fast and slow diffusing populations but had relatively little effect on the diffusion coefficients of the two populations. Precipitation of the HASE AP from THF−HClaq produced two fractions, one enriched with hydrophobe and the other correspondingly depleted relative to the global average. The fractions enriched and depleted with respect to hydrophobe exhibited diffusion coefficients similar to the fast and slow diffusing populations. We conclude that the hydrophobe is inhomogeneously distributed among the HASE AP chains, that the population enriched with hydrophobe forms more compact structures capable of faster diffusion, and that the effects of hydrophobe chain length and PEO spacer arm length on HASE AP solution viscosity are mediated by their influence on the coupling of the hydrophobe enriched population into the slow-diffusing hydrophobe-depleted population.

Polymer Adhesion vs Substrate Receptor Group Density

The effect of substrate receptor group density on polymer adhesion was investigated. Model substrates with varying −NH2 density on Al2O3 were prepared by a self-assembly of mixed amine-terminated silanes and methyl-terminated silanes. The model polymer was synthesized through a high-pressure carboxylation of polybutadiene. The polymer adhesion was determined by the fracture energy of the polymer−solid interfaces, GIC, from a T-peel test. The strong acid−base interactions between the polymer sticker groups (−COOH) and the substrate receptor groups (−NH2) at the interface caused an interesting fracture energy variation in the range of annealing times examined. At short time, GIC increased as the density of substrate receptor groups increased. However, at long time, GIC increased up to 30% receptor group coverage and then decreased with increasing coverage. A maximum in GIC occurred because the adhesive interface strength increased between the solid surface and the adsorbed chains, and simultaneously the cohesive interface strength decreased between the adsorbed chains and the neighboring free chains with increasing density. Failure occurred at the weaker of the two interface strengths. In this paper, it was shown that the polymer adhesion was not a monotonic function of the surface energetics.

Adhesion at Polymer-Solid Interfaces: Influence of Sticker Groups on Structure, Chain Connectivity and Strength

The influence of sticker groups (COOH) on the adhesion energy (G 1C) of a model carboxylated polybutadiene-amine terminated silane modified aluminum (cPBD-AIS) interface was examined using a T-peel test. An optimal COOH concentration of around 0.5 mol% was observed. At this concentration the interface possessed a maximum peel energy of 600 J/m2, which is approximately equal to the cohesive peel energy of PBD. The adhesion strength of the interface increased as the interaction parameter (°CHP-S) between COOH and the solid substrate increased. Additionally, G IC was strongly dependent on the annealing time, resulting from slow surface reorganization processes. The interface structure was explored using the self-consistent field lattice model (SCFLM) developed by Theodorou. An interphase region adjacent to the solid substrate was found as a consequence of a gradient in chain connectivity and a strong sticker group segregation near the solid surface. The modeling study provided information about how the interphase structure changed with φ and °CHP-S, explaining the experimental results well.

Interaction between small colloidal particles and molecular chains with selectively adsorbing groups: computer simulation study

Using the Monte Carlo simulation technique and the method of simulated annealing, we study interactions between small (nanometric) particles and flexible-chain polymers with sticker groups which selectively adsorb on the particles and also can strongly attract each other. For the chains with two end stickers (telechelic polymers), we find that the colloidal particles adsorbing on the polymers play the role of junction points (locks) which bind together the ends of different chains. This direct or indirect binding leads to the formation of a web-like structure throughout the sample: colloidal particles and chain stickers group into mixed clusters – “drops of a fog” – which are wrapped by polymer chains and connected by bridges. Analyzing static structure factors, we show that the selectively adsorbing telechelic polymers can affect the equilibrium spatially homogeneous distribution of colloidal particles that results in the appearance of a quasiregular structure on the intermediate scale related to the average intercluster distance. At sufficiently strong attraction between particles and chain end-groups, most of the telechelic chains (>90%) adopt either a loop-like or a stretched bridge-like conformation, the most typical morphology of the system being a combination of these two structural elements. In the mixed clusters, the colloidal particles and the chain ends pack locally on a binary grid corresponding to a local crystal-like arrangement. For the chains without attracting end-groups, we observe the formation of elongated, rugby-ball-like clusters having alternate layers of particles and adsorbing chain groups.

Polymer−Solid Interfaces: Influence of Sticker Groups on Structure and Strength

A model polymer−solid interface, aluminum- (Al-) carboxylated polybutadiene (cPBD), was designed to investigate the influence of the sticker group (−COOH) on the fracture energy (GIC). A model poly...