Homopolymer Solutions Research Articles

Stabilizing Effect of PS-b-PMMA Diblock Copolymers in PS/PMMA-Based THF-in-THF Emulsions.

We have investigated the common solvent-based emulsion composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) solutions in tetrahydrofuran in the presence of PS-b-PMMA diblock copolymers. The stabilization effect of the diblock was determined visually and by confocal laser scanning microscopy at various phase volume fractions, concentrations, and compositions of the copolymer. The behavior of PS-b-PMMA in each homopolymer solution was studied with static and dynamic light scattering. The copolymer formed micelles above a critical homopolymer concentration. Light scattering measurements showed that small amounts of the other homopolymer added to the micelle solution entered the micelles spontaneously, suggesting that the observed emulsion stability is caused by the diblock copolymer laminar layer formation covering the surface of the dispersed droplets.

Cosolvent incorporation modulates the thermal and structural response of PNIPAM/silyl methacrylate copolymers.

Polymers functionalized with inorganic silane groups have been used in wide-ranging applications due to the silane reactivity, which enables formation of covalently-crosslinked polymeric structures. Utilizing stimuli-responsive polymers in these hybrid systems can lead to smart and tunable behavior for sensing, drug delivery, and optical coatings. Previously, the thermoresponsive polymer poly(N-isopropyl acrylamide) (PNIPAM) functionalized with 3-(trimethoxysilyl)propyl methacrylate (TMA) demonstrated unique aqueous self-assembly and optical responses following temperature elevation. Here, we investigate how cosolvent addition, particularly ethanol and N,N-dimethyl formamide (DMF), impacts these transition temperatures, optical clouding, and structure formation in NIPAM/TMA copolymers. Versus purely aqueous systems, these solvent mixtures can introduce additional phase transitions and can alter the two-phase region boundaries based on temperature and solvent composition. Interestingly, TMA incorporation strongly alters phase boundaries in the water-rich regime for DMF-containing systems but not for ethanol-containing systems. Cosolvent species and content also alter the aggregation and assembly of NIPAM/TMA copolymers, but these effects depend on polymer architecture. For example, localizing the TMA towards one chain end in 'blocky' domains leads to formation of uniform micelles with narrow dispersities above the cloud point for certain solvent compositions. In contrast, polydisperse aggregates form in random copolymer and PNIPAM homopolymer solutions - the size of which depends on solvent composition. The resulting optical responses and thermoreversibility also depend strongly on cosolvent content and copolymer architecture. Cosolvent incorporation thus increases the versatility of inorganic-functionalized responsive polymers for diverse applications by providing a simple way to tune the structure size and optical response.

Dual Thermo- and pH-Responsive Block Copolymer of Poly(N-isopropylacrylamide)-block-Poly(N,N-diethylamino Ethyl Acrylamide): Synthesis, Characterization, Phase Transition, and Self-Assembly Behavior in Aqueous Solution

Doubly thermo- and pH-responsive poly(N-isopropylacrylamide)-block-poly(N,N-diethylamino ethyl acrylamide) (PNIPAM-b-PDEAEAM) with different compositions were synthesized by reversible addition–fragmentation chain-transfer (RAFT) polymerization. The properties (solubility, self-assembly behavior) of these polymers and corresponding homopolymers in solution depend on the value of pH and the protonation degree of the diethylamino moiety. The effect of the nature of the polymer chain ends also appears to be critical to fully understand this behavior. At pH 10, both PNIPAM and PDEAEAM blocks are thermoresponsive and make a cooperative contribution to phase transition, and stable spherical nanoobjects are detected as temperature rises over transition point. At pH 4, PNIPAM-b-PDEAEAM with longer PDEAEAM length displays a two-step thermoresponsive behavior; upon heating, PNIPAM chains undergo shrinkage and subsequent reorganization causing the formation of large aggregates with a positively charged shell made of PDEAEAM block in its protonated state. The aggregation processes are also particularly sensitive to kinetic considerations, and therefore, measured size of aggregates depends strongly on the history of polymer solution.

КОМПОЗИЦИОННЫЕ МАТЕРИАЛЫ НА ОСНОВЕ АЛЮМОФТОРСИЛИКАТНОГО СТЕКЛА

The article presents the results of an analytical review of the literature on glass ionomer (glass polyalkenate) cements, which are widely used in dentistry. This materials consist from the powder and liquid, which form a plastic mass at mix that sets to form a solid. The composition of the powder and liquid components of glass ionomer cement has been analyzed. The solid component is powdered calcium or strontium aluminofluorosilicate glass, the liquid component is an aqueous solution of acrylic acid homopolymer or its copolymer with methylene-succinic acid, maleic acid and other monomers. Information about the range of compositions of aluminofluorosilicate glass, raw materials and melting process parameters are represented. An analysis of the curing mechanism of this dental material is also carried out. Acid-base interaction and cross-linking of polymeric acid molecules with ions extracted from glass occur at mixing the powder and liquid components. The final microstructure of the hardened glass ionomer cement is partially decomposed glass particles embedded in a matrix of calcium and aluminum polyalkenoates and coated with a layer of silica gel. The information presented in this review may be useful for a comprehensive understanding by dentists, developers of dental materials and scientific groups conducting research in this subject area of the physicochemical process of curing this material.

Janus micro‐thread to micro‐nanodroplets using dynamic contact line lithography

AbstractDynamic contact line lithography (DCLL) is generally used for the template‐less but well‐ordered deposition of polymer micro/nanostructures from the solution of homopolymer. DCLL from the blend of several polymers in a common suitable solvent can generate rich morphologies including nanostructured Janus micro threads on a surface which might be challenging to fabricate using any other method. A blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in toluene with different compositions and concentrations are used for DCLL at a constant contact line speed of 10 μm/s. Variations of compositions and the overall concentration of polymer, engender Janus micro threads to undulated threads and multi‐layered micro/nanodroplets of PS/PMMA. Interestingly, the more soluble PS phase separates first compared to less soluble PMMA near the contact line due to the enhanced local concentration of PS during the convective flow of the solvent toward the contact line. This is also verified by DCLL using PS/PMMA blend in ethyl acetate as well. In that case, more soluble PMMA deposits first near the contact line compared to marginally less soluble PS in the solvent.

Stoichiometric versus stochastic interaction in models of liquid-liquid phase separation

Under appropriate temperature and concentration conditions, charge-neutral homopolymer solutions can segregate into two distinct phases: a polymer-dilute (solvent-rich) and a polymer-dense phase (1, 2). This phenomenon, known as liquid-liquid phase separation (LLPS), is widespread in hetero-polymeric protein solutions as well. The LLPS of folded proteins has been well known for many decades (3, 4). In contrast, the LLPS of newly found classes of proteins that do not fold into unique “native” structures, intrinsically disordered proteins (IDPs) or proteins with intrinsically disordered regions (IDRs), has been reported only in the last decade.

Unraveling the Complexity of Supramolecular Copolymerization Dictated by Triazine-Benzene Interactions.

Supramolecular copolymers formed by the noncovalent synthesis of multiple components expand the complexity of functional molecular systems. However, varying the composition and microstructure of copolymers through tuning the interactions between building blocks remains a challenge. Here, we report a remarkable discovery of the temperature-dependent supramolecular copolymerization of the two chiral monomers 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)tribenzamide (S-T) and 4,4′,4″-(benzene-1,3,5-triyl)tribenzamide (S-B). We first demonstrate in the homopolymerization of the two individual monomers that a subtle change from the central triazine to benzene in the chemical structure of the monomers significantly affects the properties of the resulting homopolymers in solution. Homopolymers formed by S-T exhibit enhanced stability in comparison to S-B. More importantly, through a combination of spectroscopic analysis and theoretical simulation, we reveal the complex process of copolymerization: S-T aggregates into homopolymers at elevated temperature, and upon slow cooling S-B gradually intercalates into the copolymers, to finally give copolymers with almost 80% alternating bonds at 10 °C. The formation of the predominantly alternating copolymers is plausibly contributed by preferred heterointeractions between triazine and benzene cores in S-T and S-B, respectively, at lower temperatures. Overall, this work unravels the complexity of a supramolecular copolymerization process where an intermediate heterointeraction (higher than one homointeraction and lower than the other homointeraction) presents and proposes a general method to elucidate the microstructures of copolymers responsive to temperature changes.

Critical Depletion, Adsorption, and Intersurface Interaction in Polymer Solutions: A Mean-Field Theory Study

Using a self-consistent field theory, we examine the thermodynamics and interfacial properties of a homopolymer solution, either close to a single hard surface or confined between two parallel surfaces, in equilibrium with a bulk reservoir. We focus on the bulk critical regime and find that various physical quantities therein exhibit qualitatively different behaviors from those in the off-critical regime. For the single-surface system, the surface-excess Γ diverges as ln|ϕb – ϕc| and ln|χc – χ| when approaching the bulk critical point, where χ and ϕb are the Flory–Huggins interaction parameter and the volume fraction of polymer segment in bulk solution, respectively, and χc and ϕc are their respective values at the critical point. Γ diverges to +∞ when the surface–polymer interaction eₛ is larger than the depletion–adsorption transition (DAT) point ec, and to −∞ when eₛ < ec. As such, the DAT at ec in the critical regime is rather sharp and ec = 0.1824 + 0.1359N–¹/² at large N. For the two-surface system, the intersurface potential W at the critical point is purely attractive for both depleted and adsorbed cases and follows a D–³ power-law decay at large intersurface separations D; when eₛ is close to ec, the strength of W becomes rather weak. This nonmonotonic dependence of W on eₛ has important experimental implications on the stability of colloidal suspensions.

Synthesis and characterization of oleic acid stabilized CdTe quantum dots and their properties as luminescence quencher of a pyridine pendented rod-coil homopolymer

Abstract We report a facile one-step non aqueous synthesis of oleic acid stabilized cadmium telluride (CdTe) quantum dots (QDs) with an average diameter of 3 nm to 4 nm by hot injection method. The synthesized oleic acid capped QDs observed by TEM were nearly spherical. The optical properties of QDs were characterized by UV-Vis absorption spectra and photoluminescence (PL) spectra. The structures of QDs and their surface passivation were further verified using transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The quenching effect of the CdTe QD was explored by addition of CdTe nanocrystals into a solution of rod-coil homopolymer (poly[10-(6-(9,9-diethyl-7-(pyridin-4- yl)-9H-fluoren-2-yl)naphthalen-2-yloxy) decyl methacrylate]) (PFNA) having pendent pyridine. The gradual addition of quantum dots to the solution of PFNA quenched the PL spectra of PFNA. This may be used to explore the coordination ability of pyridine containing homopolymer with CdTe quantum dots.

Interactions between Colloidal Particles Mediated by Nonadsorbing Polymers: Casimir and Anti-Casimir Effects

We examined a simple model system of homopolymer solutions in 3D confined between two parallel and nonabsorbing surfaces and in equilibrium with a bulk solution and accurately calculated the effective interaction between the two surfaces using both lattice Monte Carlo (MC) simulations and self-consistent field (SCF) calculations. Our results here, when compared with those in 2D (Zhang, P.; Wang, Q., Macromolecules 2019, 52, 5777), quantitatively revealed that the fluctuation-induced intermediate-range repulsion between the two surfaces (i.e., the anti-Casimir effect) is about 1 order of magnitude stronger than the repulsion due solely to the finite chain length given by the SCF theory, is weaker but occurs over a broader range of surface separation in 3D than in 2D, and decreases with decreasing solvent quality. We also found for the first time a long-range attraction between the two surfaces (i.e., the Casimir effect) near the critical point of the bulk solution in both MC simulations and SCF calculations.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization.

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO100PO65EO100) and Pluronic P123 (EO19PO69EO19), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Effect of an electric field on the stability of binary dielectric fluid mixtures.

We consider the phase stability of binary fluid mixtures with constituents of contrasting dielectric properties in the presence of a static applied electric field, E0. The dielectric fluid is modeled using a recently developed field-theoretic representation for the equilibrium behavior of a system of polarizable molecular species [J. M. Martin et al., J. Chem. Phys. 145, 154104 (2016)]. The dielectric displacement of the fluid, D, is obtained from a direct E0 derivative of the fluid's free energy, illuminating coupled structural and electrostatic fluctuations that manifest in the dielectric properties of the fluid. Linearizing D with respect to E0 yields an explicit, molecularly based expression for the dielectric constant of the fluid mixture, ϵ, through the relation D = ϵE0. In the linear response regime, the composition dependence of ϵ completely specifies the applied field-dependent contribution to the fluid's miscibility, which we enumerate as a contribution χE to a Flory interaction parameter. Using a Gaussian approximation to the field theory, we obtain an expression for χE that relates structural and electrostatic contrast between dissimilar molecules to miscibility in the presence of an applied field. Specifically, contrast between wavevector-dependent, single-molecule correlation functions, Λ^A/B(k), emerges as a necessary ingredient for electric field-induced mixing, corresponding to χE < 0. The character of χE is considered in three classes of binary systems: a binary simple fluid, a homopolymer blend, and a homopolymer solution. Within each system, the form for Λ^A/B accounts for molecular architecture effects, such as chain connectivity. Our findings elucidate the conditions for which one should expect electric field induced mixing or demixing for each class of mixture.

Self-assembly in Solutions of Amphiphilic Homopolymers: Computer Modeling and Analytical Theory

The main feature of amphiphilic homopolymers is the effective surface activity of their monomer units, due to which, in selective solvent, they can aggregate into various structures, some of which ...

Tuning Pore Dimensions of Mesoporous Inorganic Films by Homopolymer Swelling.

The functionality and applications of mesoporous inorganic films are closely linked to their mesopore dimensions. For material architectures derived from a block copolymer (BCP) micelle coassembly, the pore size is typically manipulated by changing the molecular weight corresponding to the pore-forming block. However, bespoke BCP synthesis is often a costly and time-consuming process. An alternative method for pore size tuning involves the use of swelling agents, such as homopolymers (HPs), which selectively interact with the core-forming block to increase the micelle size in solution. In this work, poly(isobutylene)-block-poly(ethylene oxide) micelles were swollen with poly(isobutylene) HP in solution and coassembled with aluminosilicate sol with the aim of increasing the resulting pore dimensions. An analytical approach implementing spectroscopic ellipsometry (SE) and ellipsometric porosimetry (EP) alongside atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) in transmission and grazing-incidence (GISAXS) modes enabled us to study the material evolution from solution processing through the manifestation of the mesoporous inorganic film after BCP removal. The in-depth SE/EP analysis evidenced an increase of more than 45% in mesopore diameter with HP swelling and a consistent scaling of the overall void volume and number of pores. Importantly, our analytical toolbox enabled us to study the effect of swelling on the connecting necks between adjacent pores, with observed increases as high as ≈35%, offering novel pathways to sensing, electrochemical, and other mass-transfer-dependent applications.

Creation of Centimeter-Sized 2 D Crystalline Film by Crystallization of Homopolymer in Solution.

The 2 D assembly of polymers to form free-standing and large crystalline films is quite appealing but very challenging. Although there have been some works using interface templates, reports of in situ assembly in solution are still rare. Herein, a simple strategy is developed for the creation of a free-standing and centimeter-sized 2 D crystalline polymer film through crystallization of an amphiphilic brush polydiacetylene (PDA) in solution. The film exhibits good shape memory, a low dielectric constant, and good carrier mobility. This strategy may be applied extensively to produce a variety of other macroscopic 2 D crystalline polymer films for applications in electronics, catalysis, and so on.

Coherent states field theory in supramolecular polymer physics.

In 1970, Edwards and Freed presented an elegant representation of interacting branched polymers that resembles the coherent states (CS) formulation of second-quantized field theory. This CS polymer field theory has been largely overlooked during the intervening period in favor of more conventional "auxiliary field" (AF) interacting polymer representations that form the basis of modern self-consistent field theory (SCFT) and field-theoretic simulation approaches. Here we argue that the CS representation provides a simpler and computationally more efficient framework than the AF approach for broad classes of reversibly bonding polymers encountered in supramolecular polymer science. The CS formalism is reviewed, initially for a simple homopolymer solution, and then extended to supramolecular polymers capable of forming reversible linkages and networks. In the context of the Edwards model of a non-reacting homopolymer solution and one and two-component models of telechelic reacting polymers, we discuss the structure of CS mean-field theory, including the equivalence to SCFT, and show how weak-amplitude expansions (random phase approximations) can be readily developed without explicit enumeration of all reaction products in a mixture. We further illustrate how to analyze CS field theories beyond SCFT at the level of Gaussian field fluctuations and provide a perspective on direct numerical simulations using a recently developed complex Langevin technique.

Studies on the phase transition of hydrogels and aqueous solutions of thermosensitive polymers

In this review, our recent studies on the phase transition of hydrogels and aqueous solutions of thermosensitive homopolymers and copolymers are briefly summarized. On the basis of the concept of cooperative hydration, which is defined as the association-dissociation of water molecules bound to a polymer chain with a positive correlation between adjacent bound water molecules, we theoretically examine the following phenomena: (i) the high-temperature collapse of poly(N-isopropylacrylamide) (PNIPAM) gels in water; (ii) the reentrant volume phase transition of PNIPAM gels in mixed solvents of water/methanol; (iii) the temperature dependence of the swelling behavior of PNIPAM microgels in mixed solvents of water/methanol, the selective solvent adsorption of the gels and the selective solvent binding to the polymer chains; and (iv) the nonlinear depression of the lower critical solution temperature of thermosensitive copolymers in water as the monomer composition is varied. Our theoretical results are compared with the experimental data, and the molecular mechanisms are discussed. Theoretical models for thermo-sensitive hydrogels in pure water and in mixed solvent of water and methanol, and for thermo-sensitive copolymer in water are developed based on the concept of cooperative hydration of thermo-sensitive water-soluble polymers. The high-temperature collapse in water and the reentrant volume phase transition in water/methanol mixtures of poly(N-isopropylacrylamide) gels, and the phase behavior of statistical random copolymers of N-isopropylacrylamide and N,N-diethylacrylamide are theoretically studied.

Internal friction in an intrinsically disordered protein-Comparing Rouse-like models with experiments.

Internal friction is frequently found in protein dynamics. Its molecular origin however is difficult to conceptualize. Even unfolded and intrinsically disordered polypeptide chains exhibit signs of internal friction despite their enormous solvent accessibility. Here, we compare four polymer theories of internal friction with experimental results on the intrinsically disordered protein ACTR (activator of thyroid hormone receptor). Using nanosecond fluorescence correlation spectroscopy combined with single-molecule Förster resonance energy transfer (smFRET), we determine the time scales of the diffusive chain dynamics of ACTR at different solvent viscosities and varying degrees of compaction. Despite pronounced differences between the theories, we find that all models can capture the experimental viscosity-dependence of the chain relaxation time. In contrast, the observed slowdown upon chain collapse of ACTR is not captured by any of the theories and a mechanistic link between chain dimension and internal friction is still missing, implying that the current theories are incomplete. In addition, a discrepancy between early results on homopolymer solutions and recent single-molecule experiments on unfolded and disordered proteins suggests that internal friction is likely to be a composite phenomenon caused by a variety of processes.

Thermoreversible crystallization-driven aggregation of diblock copolymer nanoparticles in mineral oil.

A poly(behenyl methacrylate)37 (PBeMA37) macromolecular chain transfer agent is utilized for the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) directly in mineral oil at 90 °C. Polymerization-induced self-assembly (PISA) occurs under these conditions, yielding a series of sterically-stabilized PBeMA37-PBzMA x diblock copolymer spheres of tunable diameter as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies. Rheological studies indicate that a relatively transparent, free-flowing, concentrated dispersion of non-interacting 32 nm PBeMA37-PBzMA100 spheres at 50 °C forms a turbid, paste-like dispersion on cooling to 20 °C. Turbidimetry and differential scanning calorimetry (DSC) studies conducted on solutions of PBeMA37 homopolymer in mineral oil suggest that this switchable colloidal stability is linked to crystallization-induced phase separation exhibited by this stabilizer block. Indeed, variable-temperature small-angle X-ray scattering (SAXS) indicates that a loose mass fractal network of strongly interacting spheres is formed on cooling to 20 °C, which accounts for this thermoreversible sol-gel transition. Moreover, SAXS, DSC and wide-angle X-ray scattering (WAXS) analyses indicate that the behenyl (C22H45) side-chains first form crystalline domains comprising adjacent stabilizer chains within individual spherical nanoparticles, with subsequent crystallization between neighboring nanoparticles leading to the formation of the mass fractal aggregates.

Dynamic surface properties of poly(methylalkyldiallylammonium chloride) solutions

Dynamic surface properties of aqueous solutions of cationic polyelectrolytes poly(hexylmethyldiallylammonium chloride) (PHMDAAC) and poly(butylmethyldiallylammonium chloride) (PBMDAAC) differ significantly from the properties of the solutions of other charged homopolymers, for example, sodium poly(sterenesulfonate) (PSS) and poly(dimethyldiallylammonium chloride) (PDMDAAC). At the same time, the obtained results are in agreement with the predictions of the theory of the dilational surface viscoelasticity of polymer solutions. The dynamic surface elasticity of PHMDAAC solutions increases monotonically with the surface age up to about 30 mN/m while the increase of the solution ionic strength results in non-monotonic kinetic dependencies and in low values (<5 mN/m) of the surface elasticity close to equilibrium. The surface activity of PBMDAAC is much lower and the deviations of the surface elasticity from zero exceed error limits only slightly in the investigated concentration range (≤0.2 wt%).