Side Chain Density Research Articles

Retardation effect of PCE superplasticizers with different architectures and their impacts on early strength of cement mortar

As the most effective superplasticizer, the comb-like PCE polymers also severely retard early cement hydration and hence decelerate early strength growth of concrete, which is undesired in some applications. In this study, a series of PCEs with different molecular architectures, including varied side chain length and density were synthetized by co-polymerizing acrylic acid and α-methallyl-ω-hydroxy poly(ethylene glycol) ether. Impacts of the obtained PCEs on cement hydration and early strength of mortar were investigated. Results show that adsorption of PCEs on cement grains is highly dependent on polymer architectures. Higher side chain length and density lead to lower adsorption amount and consequently higher early strength of mortar. It is interestingly found that the retardation effect of the PCEs on cement hydration is simply proportion to their absolute adsorption amounts on cement surface, while the complexation of R−COO− group with Ca2+, which is independent on polymer architectures, plays a minor role.

Well-Defined Alkyl Functional Poly(Styrene-co-Maleic Anhydride) Architectures as Pour Point and Viscosity Modifiers for Lubricating Oil

A series of well-defined poly(styrene-co-maleic anhydride) copolymers (PSMA) allowing controlled grafting density and distribution of long alkyl side chains (C12 and C22) was synthesized and invest...

Dealing with workability loss challenge in SCC mixtures incorporating natural pozzolans: A study of natural zeolite and pumice

Substituting portland cement with natural zeolite (NZ) and pumice in self-consolidating concrete (SCC) is used to improve the workability and hardened properties of mixtures. The workability retention of SCC incorporating these natural pozzolans has remained a challenge in the literature. In this study, different methods of workability retention improvement on the natural pozzolan-SCC mixtures were investigated. These methods include the use of polycarboxylate with larger molecular weight and side chain density, retempering with superplasticizer (SP), retempering with withhold water, and a combination of retarder and SP. The fresh and hardened properties of the NZ and pumice-incorporated mixtures were investigated through measuring workability retention, setting time, and compressive strengths, in two ratios of water-to-cementitious materials (w/cm). Results show that the SCC mixtures incorporating NZ had lower setting time in comparison to the SCCs without natural pozzolans, although the setting time of SCC contained pumice increased. The NZ-incorporated SCCs required a higher dosage of SP for retempering however the pumice contained SCCs required lower SP than the reference due to the low-polymer adsorption of pumice-blended cement. The slump loss in SCC mixture without pozzolan (Ref-0.36) was more severe than the mixtures containing NZ. The reduction in compressive strength of mixtures treated with different retempering methods was insignificant but more tangible when superplasticizer and retarder were used. A larger quantity of SP was required for retempering the SCCs with retarder and SP compared with the those retempered with SP only. The increase or decrease in the SCC compressive strength in case of using retarder and SP for SCC retempering purpose was dependent on the amount of pozzolan replacement and the w/cm ratio in the mixtures. Overall, in w/cm ratio of 0.40, the SCC mixtures incorporating 10 and 15% NZ and pumice, respectively, possessed as the optimal mixtures considering the slump loss and the compressive strength.

Influence of the polymer structure of polycarboxylate-based superplasticizers on the intercalation behaviour in montmorillonite clays

The influence of polymeric structure of polycarboxylate-ether (PCE) based superplasticizers on the intercalation behavior in sodium montmorillonite clay (Na-MNT) is investigated by performing in-situ X-ray diffraction (XRPD) on fresh, unaltered clay pastes. The use of this technique reveals the real influence of the PCE structure and of the PCE/clay dosage ratio on the expansion profile of the clay. This is not observed with the traditional XRPD methodology performed on dried clay pastes, which shows the same values of d-spacing despite using polymers of diverse structures. It is observed that PCE polymers with long side chains and high side chain density result in larger expansion. Additionally, polymers with a high anionic charge saturate the interlaminar space of montmorillonite at a lower dosage. The experimental results also indicate that clay exfoliation is critical in the intercalation process and the exfoliation tendency of the clay is influenced by the structure of PCE polymers.

The Critical Role of Electron‐Donating Thiophene Groups on the Mechanical and Thermal Properties of Donor–Acceptor Semiconducting Polymers

AbstractOrganic semiconducting donor–acceptor polymers are promising candidates for stretchable electronics owing to their mechanical compliance. However, the effect of the electron‐donating thiophene group on the thermomechanical properties of conjugated polymers has not been carefully studied. Here, thin‐film mechanical properties are investigated for diketopyrrolopyrrole (DPP)‐based conjugated polymers with varying numbers of isolated thiophene moieties and sizes of fused thiophene rings in the polymer backbone. Interestingly, it is found that these thiophene units act as an antiplasticizer, where more isolated thiophene rings or bigger fused rings result in an increased glass transition temperature (Tg) of the polymer backbone, and consequently elastic modulus of the respective DPP polymers. Detailed morphological studies suggests that all samples show similar semicrystalline morphology. This antiplasticization effect also exists in para‐azaquinodimethane‐based conjugated polymers, indicating that this can be a general trend for various conjugated polymer systems. Using the knowledge gained above, a new DPP‐based polymer with increased alkyl side chain density through attaching alky chains to the thiophene unit is engineered. The new DPP polymer demonstrates a record low Tg, and 50% lower elastic modulus than a reference polymer without side‐chain decorated on the thiophene unit. This work provides a general design rule for making low‐Tg conjugated polymers for stretchable electronics.

Effects of the side chain density of polycarboxylate dispersants on dye dispersion properties

Comb‐like polycarboxylates were synthesised by copolymerisation of methacrylic acid and nonylphenol polyethylene glycol methacrylate ester, and can be used as dye dispersants. In order to achieve good dispersive ability, three polycarboxylates were synthesised, each having a different side chain density. The side chain density of polymers was controlled by different ratios of monomers in the copolymerisation process. Acidic polymers were neutralised using sodium hydroxide. These polymers exhibit good dispersing performance, such that carboxylate groups are adsorbed onto the dye particle surface and the side chains enable the formation of a thick layer, thus providing the steric hindrance effect. Improvement of dye dissolution in the presence of polycarboxylates was studied. Polymers with a lower side chain density demonstrated a higher dye dissolution in water, which could be as a result of more effective adsorption of dispersant on the dye surface (CI Disperse Blue 79). The dyeing performance of the prepared dye dispersions on polyester was investigated. Spectrophotometric analysis of dyed fabrics using synthesised polycarboxylates demonstrates that there should be an optimum side chain density of polymer in order to control both dye solubility and dispersive ability. The result of turbidimetry and particle size analysis have proven this phenomenon. A comb‐like polycarboxylate with optimum side chain density was a better dye dispersant compared with a commercial sodium naphthalene sulphonate compound, as a result of its better heat stability.

Influence of Grafting Density and Distribution on Material Properties Using Well-Defined Alkyl Functional Poly(Styrene-co-Maleic Anhydride) Architectures Synthesized by RAFT

Poly(styrene-co-maleic anhydride) copolymers (PSMA) with controlled number and distribution of maleic anhydride (MAnh) units were synthesized by reversible addition–fragmentation chain transfer polymerization using chain-transfer agents (CTA) suitable for industrial scale processes. Linear- and star-shaped alternating PSMA polymers were prepared in a single-step synthesis, while a one-pot sequential chain-extension strategy was utilized to prepare diblock, multiblock, and multisite copolymer architectures. A library of grafted PSMAs with controlled density and distribution of side chains was achieved by the subsequent grafting of long aliphatic alcohol chains (C22) to the MAnh units. The influence of structure, composition, and long alkyl chain addition on PSMAs behavior in solution was studied with triple-detection size exclusion chromatography, while their thermal properties were examined by thermogravimetric analysis and differential scanning calorimetry. Overall, the side chain density and distributio...

Synthesis of a well-defined alternating copolymer of 1,1-diphenylethylene and tert-butyldimethylsilyloxymethyl substituted styrene by anionic copolymerization: toward tailored graft copolymers with controlled side chain densities

Well-defined alternating copolymers comprising 1,1-diphenylethylene (DPE) and styrene derivative having sterically bulky tert-butyldimethylsilyloxymethyl group at the meta position (St-TBS) were successfully synthesized.

Single-Chain Conformational Characteristics of Comb-Like Polyelectrolytes: Molecular Dynamics Simulation Study

The single-chain conformation of a model comb polyelectrolyte, in which the electric charges are located on the last monomer of side chains, has been studied using molecular dynamics simulations. The model chain has a hydrophobic backbone and hydrophilic side chains. The influence of parameters such as the length of backbone and side chains, the grafting density of side chains, flexibility of the chain and different strengths of backbone hydrophobicity have been investigated. At high grafting density of side chains, a transition from turn to pearl-necklace and finally to globular conformation is observed by increasing the hydrophobicity. Radius of gyration (Rg) of the backbone depends linearly on the number of backbone monomers at low values of the backbone hydrophobicity, but at high values of the backbone hydrophobicity, because of the appearance of turn-like segments between successive globular sections in the pearl-necklace structure, the scaling exponent of Rg versus N is larger. Also, the chain flexibility affects the backbone conformation significantly. The increase of the persistence length leads to the appearance of the folded and then the extended conformations. In addition to the statistical properties of the chains, the investigation of the relaxation of the chains conformation shows that, the backbone takes almost its final conformation in the early time steps of the simulation for all conditions. It means that the relaxation time of the chain is relatively short (fast relaxation).

Automation and assessment of de novo modeling with Pathwalking in near atomic resolution cryoEM density maps.

With the rapidly growing number of macromolecular structures solved to near-atomic resolution using electron cryomicroscopy (cryoEM), map interpretation and model building directly from the density without the use of structural templates has become increasingly important. As part of the 2015/2016 Map and Model Challenge, we attempted to assess our latest de novo modeling tool, Pathwalking, in terms of performance and usability, as well as identify areas for future improvements. In total, we applied Pathwalking to six density maps between 3 and 4.5 Å resolution selected from the challenge data sets. In five of the six cases, Pathwalking was able to accurately determine the protein fold and in three of these cases, the final all atom model had less than 1.6 Å RMSD when compared to the known structure. Model building and refinement was nearly completely automated, used default parameters and took less than 30 min to complete a refined all atom model. A direct outgrowth of this work was a more streamlined automated command line Pathwalking utility, as well as a novel sequence assignment and optimization routine, which attempts to register sidechain density with expected side chain volume. In total, Pathwalking offers a nearly complete, robust and efficient method for constructing atomistic protein structures directly from a density map without the aid of a template.

Coarse-Grained Molecular Dynamics Study of Ionomer Aggregation and Network Formation in Dilute Solution

The presented work comprises a computational study of self-assembly in dilute solution of Nafion-type perfluorosulfonic acid (PFSA) ionomers. We employ coarse-grained molecular dynamics (CGMD) to investigate the formation of ionomer bundles [1] and study the assembly of ionomer bundles into a bundle network upon increasing ionomer concentration. Formation of this supramolecular network is experimentally indicated by a markedly increased viscosity [2]. Evolution of a gel-like structure in the aqueous solutions also studied experimentally by Cirkel et al. [3] and Rubatat et al. [4], revealing more details about transport properties, stability, and water sorption properties of the network structure of interconnected ionomer bundles in Nafion membranes. Simulation of the interconnected, gel-like ionomer state provides opportunities to scrutinize different proposed structural models of ionomer membranes and assess changes in bundle size and network connectivity as functions of backbone hydrophobicity, side chain density, counterion valence, and strength of electrostatic interaction between anionic head groups at ionomer sidechains.

Impact of the charge density on the behaviour of polycarboxylate ethers as cement dispersants

The charge density of polycarboxylate ethers (PCEs) is the driver for adsorption of these polymers on the surface of hydrating Portland cement, which is the necessary step for the PCE to disperse and plasticise Portland-based materials. The charge density of a PCE is commonly considered the result of a certain molecular architecture and the complement of the sidechain density, regardless the synthetic route chosen to produce the comb polymer. Hence, its effect is normally masked by the impact of different structures. In this work, three sets of three polymers each have been prepared by esterification of three similarly sized but different in constitution polyacrylic acids. Within each set, the reaction conditions have been tuned to promote a more or less accentuated acid function loss. The resulting PCEs all bear the same structure and conformation but substantially differ in charge density. The so-isolated molecular feature has been studied through its impact on adsorption extent and rate, chemical stability, calorimetric and rheological characteristics of cement paste. It is shown that the charge density has a wide impact on the performance of PCEs as superplasticisers. Its modification heavily affects the adsorption behaviour and can turn the same structure to behave as either strong water reducer or workability extender, with a limited effect on the heat signature of the cement paste. Furthermore, some insights are disclosed regarding reactivity of polyacrylic acids towards esterification, selectivity of ester formation and resulting chemical stability.

Synthesis and characterization of lignin‐based cationic dye‐flocculant

ABSTRACTKraft lignin derivatives having cationic poly 2‐(trimethylamino)ethyl methacrylate side chains were synthesized and their property as dye‐flocculant was investigated. Lignin‐based flocculants having three types of side chain densities and three types of side chain lengths were synthesized by esterification of the lignin hydroxyl groups with bromoisobutyryl groups, atom transfer radical polymerization using 2‐(dimethylamino)ethyl methacrylate, and quaternization of the amino groups. Dye removal test was performed using three organic dyes and the obtained lignin‐based flocculants. The results indicated that the density and the length of the side chains obviously affected the flocculation behavior. When the flocculants containing the same nitrogen amount were compared, the flocculation performance was improved with the increase of the side chain length within the samples having low and middle side chain densities. In the case of the samples having high side chain density, the most efficient sample was not the sample having the longest side chain. Most of the lignin‐based flocculants removed dyes more efficiently than the poly 2‐(trimethylamino)ethyl methacrylate homopolymer. From these results, it was suggested that lignin has a potential character as the core molecule to design the high‐efficient dye‐flocculant. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46611.

Breaking the Bimolecular Crystal: The Effect of Side-Chain Length on Oligothiophene/Fullerene Intercalation

Polymer/fullerene bimolecular crystal formation has been investigated using a variety of conjugated polymers and fullerenes to understand the design rules that influence donor–acceptor interaction. Modifications of the polymer by varying the substitution side-chain position, density, and branching have demonstrated the importance of the “pocket” dimensions (free volume between side chains where the fullerene resides) for controlling intercalation. Yet the effect of pocket height has not been systematically explored because of the solubility limitations in polymers. In this report, we present an experimental investigation into the effect of the pocket height by synthesizing poly[2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene] dimers with varied side chain lengths and track the morphological changes of the dimer/fullerene blends using grazing-incidence X-ray scattering, thermal measurements, and photoluminescence quenching. We identify two regimes: (1) oligomers with side chains greater than or equal t...

The properties of cement systems superplasticized with methacrylic ester-based polycarboxylates

Methacrylic ester-based polycarboxylate superplasticizers of methoxypolyethylene glycol metacrylate-co-methacrylic acid (mPEGMA-co-MAA) with various side-chain density and side-chain length were synthesized, characterized and their impacts on workability, rheology, setting time and mechanical strengths of cement systems were studied. The results showed that, synthesized copolymers change the rheological behaviour of cement suspensions to shear thickening and, SPs with low side chain densities increase fluidity, fluidity retention and strengths of samples higher than their counterparts. Additionally, polycarboxylates retard the hydration of cement and low triethanol-amine dosages can be preferred as an accelerator for cold weather applications or for early mechanical strengths of cement systems.

Automatic Building of Protein Atomic Models from Cryo-EM Maps

Cryo-electron microscopy (Cryo-EM) has emerged as a powerful method to obtain electron density maps of protein assemblies. However, reconstruction of atomic models from near atomic resolution (3-5 Å) cryo-EM maps is still challenging. Several tools developed for X-ray crystallography are widely used to interpret high resolution EM maps (around 3 Å), but poorly resolved side-chain densities hamper sequence attribution by automatic procedures at lower resolution. Furthermore, segmentation of EM maps into subunits remains a difficult problem when no structures of these subunits exist, or when conformational changes occur between the isolated and complexed form of the subunits. To tackle these issues, we have developed a graph-based method to thread most of the C-α trace of the protein backbone into the EM map. The EM density is described as a weighted graph such as the resulting minimum spanning tree encompasses the high density region of the map. A pruning algorithm is then applied to clean the tree and find the most probable positions of the C-α atoms, using sidechain density when available, in the form of C-α trace fragments. By complementing experimental EM maps with contact predictions from sequence co-evolutionary information, we demonstrate that our approach is able to correctly segment EM maps into individual subunits and recover most of the sequence attribution to generate full-atom models.

Hairy and Slippery Polyoxazoline-Based Copolymers on Model and Cartilage Surfaces.

Comb-like polymers presenting a hydroxybenzaldehyde (HBA)-functionalized poly(glutamic acid) (PGA) backbone and poly(2-methyl-2-oxazoline) (PMOXA) side chains chemisorb on aminolized substrates, including cartilage surfaces, forming layers that reduce protein contamination and provide lubrication. The structure, physicochemical, biopassive, and tribological properties of PGA-PMOXA-HBA films are finely determined by the copolymer architecture, its reactivity toward the surface, i.e. PMOXA side-chain crowding and HBA density, and by the copolymer solution concentration during assembly. Highly reactive species with low PMOXA content form inhomogeneous layers due to the limited possibility of surface rearrangements by strongly anchored copolymers, just partially protecting the functionalized surface from protein contamination and providing a relatively weak lubrication on cartilage. Biopassivity and lubrication can be improved by increasing copolymer concentration during assembly, leading to a progressive saturation of surface defects across the films. In a different way, less reactive copolymers presenting high PMOXA side-chain densities form uniform, biopassive, and lubricious films, both on model aminolized silicon oxide surfaces, as well as on cartilage substrates. When assembled at low concentrations these copolymers adopt a "lying down" conformation, i.e. adhering via their backbones onto the substrates, while at high concentrations they undergo a conformational transition, assuming a more densely packed, "standing up" structure, where they stretch perpendicularly from the substrate. This specific arrangement reduces protein contamination and improves lubrication both on model as well as on cartilage surfaces.

Photocatalytically active coatings for cement and air lime mortars: Enhancement of the activity by incorporation of superplasticizers

Coatings made with water dispersions of different nano-particles of photocatalytic additives (titania and titania doped with iron and vanadium) were prepared with diverse superplasticizers, SPs, to optimize the atmospheric NO removal efficiency when applied onto cement- and air-lime mortars. The use of different polycarboxylate-based superplasticizers (52IPEG, 23APEG and 45PC6) prevented nano-particles from agglomeration. The steric hindrance, provided by a large density and length of side chains, was ascertained as the most effective repulsion mechanism and 52IPEG was the most efficient SP. In PC- and air-lime mortars, the coatings with polycarboxylate-based SPs improved the NO removal rates as compared with the SP-free coating: an average increase of NO degradation by 15% under UV and by 76% under solar light was found. This finding was related to the drop in the agglomeration of the photocatalysts, with more exposed active sites and a decrease of the electron-hole recombination rates. Capillary water absorption and water vapour permeability values showed that the coatings did not alter the performance of the mortars. SEM examination showed that the use of SPs enhanced the distribution of the photocatalysts yielding thinner coating layers and boosting the percolation of the active material within the mortars. Accelerated weathering showed a moderate reduction of NO removal efficiency. Coating with 52IPEG was the most efficient in preserving the activity. Measurements of Ti content showed a low washout of the TiO2 nano-particles, supporting the long-run activity of these coatings.

Novel branched polymers and their structural effects on intercalation into Na-MMT and silica fume suspensions

Various branched polymers with different functionalities and side chains were synthesized as dispersant and their molecular structures were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance, and thermogravimetric analysis (TGA) methods. It was found that the amount of side chain and kind of acidic or ionic functions had influences on the properties of the dispersants. The effect of side chain density of the dispersants on the intercalation of sodium montmorillonite (Na-MMT) was also investigated. The results of X-ray diffraction, and FTIR and TGA analyses showed that the branched polymers with a higher amount of side chains and acidic functions were suitable to provide efficient intercalation and adsorption. In addition, a weak intercalation of dispersant with a lower side chain density and neutral functions into the Na-MMT interlayer was observed. The role of side chain density and acidic/neutralize functionalities of dispersants on both the yield stress and viscosity of reactive silica fume suspensions was investigated. It was found that the dispersant with acidic functionalities and low amount of side chains increased the yield stress and viscosity. A lower viscosity was also recorded for the suspensions in the presence of Na-MMT. Moreover, the suspension prepared by the dispersant with a high side chain density exhibited higher fluidity and lower viscosity.

Selective sorting of semiconducting single-walled carbon nanotubes using thienylenevinylene-based conjugated polymers with high alkyl side-chain density

The demand for high-purity semiconducting single-walled carbon nanotubes (sc-SWNTs) has increased considerably with the aim of utilizing their superior properties in a range of future applications. Among post-sorting methods, conjugated polymers have been regarded as one of the candidates to selectively isolate sc-SWNTs with uniform electrical properties. Herein, we demonstrate the ability to selectively sort two types of SWNTs by the two polymers PCTV18T and PC12TV18T, which have different alkyl side-chain densities. PC12TV18T, with a high alkyl chain density, shows great sorting ability for both high-pressure carbon monoxide and plasma-torch-grown SWNTs with a weight ratio of almost 1:1 in toluene solution. In addition, it is found that PC12TV18T selectively sorts sc-SWNTs with the high purity. The chirality and diameters of the enriched sc-SWNTs are further confirmed by Raman spectroscopy and photoluminescence excitation/emission mapping. Finally, we fabricate bottom gate/bottom contact thin-film transistors using the enriched sc-SWNTs as semiconductors to verify the electrical performance. Devices with well-percolated sc-SWNT networks displayed p-dominant properties with average charge-carrier mobilities of 2.05 cm2 V−1 S−1 and 9.87 cm2 V−1 S−1 and on/off current ratios of approximately 104 and 105 for high-pressure carbon monoxide and plasma-torch-grown SWNTs, respectively.