Assembly Of Polymer Chains Research Articles

Design of hydrophobic polymer brush for mitigation of membrane wetting in membrane distillation- computer simulation

Defined as an assembly of polymer chains which are tethered by one end to a surface or an interface, polymer brushes have found many applications. In particular, grafting of hydrophilic polymer brushes to the membrane surface was used to mitigate fouling of filtration membranes. As well, hydrophobic polymer brushes were grafted on top of a solid substrate to be used for organic selective pervaporation. In this work, grafting of hydrophobic brushes to the surface of membranes for membrane distillation (MD) is proposed to prevent MD membranes from wetting. This is not an experimental work but a computer simulation of designing the polymer brush or patterned polymer brush to optimize their effect on wetting prevention. It was found that such an effect increases with an increase in the distance between brushes, the contact angle and the radius of the cylindrical polymer brush. Considering the decrease in the effective area of the membrane used for vapor permeation by grafting of polymer brush, the optimal distance between the brushes was found to be twice as large as the brush diameter for millimeter-sized brush and three times as large as the brush diameter of micro- or nanometer sized brushes.

Interplay between self-assembly and phase separation in a polymer-complex model.

We present a theoretical model for predicting the phase behavior of polymer solutions in which phase separation competes with oligomerization. Specifically, we consider scenarios in which the assembly of polymer chains into stoichiometric complexes prevents the chains from phase-separating via attractive polymer-polymer interactions. Combining statistical associating fluid theory with a two-state description of self-assembly, we find that this model exhibits rich phase behavior, including reentrance, and we show how system-specific phase diagrams can be derived graphically. Importantly, we discuss why these phase diagrams can resemble-and yet are qualitatively distinct from-phase diagrams of polymer solutions with lower critical solution temperatures.

Fabrication of hierarchical porous polymer particles via blending strategy of water and polymer mixture

AbstractHierarchical porous polymer particles (HPPPs) from the assembly of polymer chains have attracted increasing interest because of their prospective applications in drug delivery and catalysis. This work utilized a blending strategy of polymer mixture in mixed solvents to fabricate HPPPs with adjustable pore structures. Firstly, using methacrylic acid (MAA) and methyl methacrylate (MMA) with a precise ratio, a copolymer solution of P(MMA‐MAA) was prepared in a mixed solvent of ethanol and water. Then, styrene (St) was added stepwise along with polymerization for achieving a translucent polymer mixture. Further, a quantitative amount of the polymer mixture and six‐fold volume of water were rapidly mixed with vortex oscillation. The HPPPs were formulated eventually by the assembly of hydrophilic P(MMA‐MAA) copolymers and hydrophobic PSt homopolymers, as well as micelles comprised of P(MMA‐MAA) copolymer and low‐polarity solvent. The size and number of nanopores were effectively regulated by the solvent polarity, polymerization temperature and monomer ratios. Moreover, the resultant HPPPs exhibited a hierarchical porous structure, having broad application in biomedical and environmental sciences. © 2022 Society of Industrial Chemistry.

Inorganic polymers made directly from silica

A novel approach is presented in which silica is used as a source for the synthesis of decarbonized (silicate-based) inorganic polymers. Natural silica (e.g., sand) is envisaged as an assembly of polymer chains and these chains are “extracted” from silica. This is accomplished by using a two-step method: (1) silica is converted to silicate glass, (2) silicate glass is converted to silicate polymer. The resulting materials have Tg values as low as 150 oC and show various characteristics of polymers. The key to the success of this method is the use of ionic liquid, which works as an ionic “plasticizer.”

High-Performance Adhesives Resulting from Spontaneous Formation of Nanogels within Miniemulsion Particles

Molecular structure plays a crucial role in determining the final properties of pressure-sensitive adhesives. Here, we demonstrate that the molecular structure of polyurethane/(meth)acrylic hybrids synthesized by miniemulsion photopolymerization changes during storage of the dispersion at room temperature because of the spontaneous formation of nanogels by the assembly of polymer chains within the polymer particles. Analysis of the nanogel structure by asymmetric-flow field-flow fractionation allows identification of the molecular structure that provides the unusual combination of high tack adhesion and excellent shear resistance at high temperature [maximum value of the shear-adhesion failure temperature (SAFT) test, >210 °C].

Solvent Based Hydrogen Bonding: Impact on Poly(3-hexylthiophene) Nanoscale Morphology and Charge Transport Characteristics

We demonstrate that supramolecular assembly and subsequent enhancement of charge transport characteristics of conjugated polymers can be facilitated simply by adding small amounts of a more volatile poor solvent, which can hydrogen bond with the majority solvent. Addition of up to 2 vol % acetone to a precursor solution of poly(3-hexylthiophene) (P3HT) in chloroform leads to approximately a 4-fold increase in P3HT field-effect mobility. The improvement is associated with hydrogen bonding interactions between acetone and chloroform which decrease the evaporation rate of the mixed solvent. P3HT is less soluble in the binary solvent than in the more readily vaporized chloroform component, and this characteristic enables the supramolecular assembly of P3HT chains at the nanoscale. Two-dimensional molecular ordering of the polymer film was controlled by varying the quantity of poor solvent added to the precursor solution, and the correlation between field-effect mobility and molecular ordering was investigated. Hansen solubility parameters were used to systematically understand how the solvent mixture enhances the alignment and assembly of polymer chains and influences subsequent thin film properties. The value of the relative energy difference (RED) of the solvent with respect to P3HT increased from less than 1 to more than 1 during film formation, which indicates that the solvent characteristics are initially those of a good solvent but transform into those of a poor dissolution medium. A mechanistic illustration of the molecular ordering process during film formation is postulated.

Surface functionalization by smart binary polymer brushes to tune physico-chemical characteristics at biointerfaces

AbstractPolymer brushes consist of an assembly of polymer chains that are attached by one end to the surface with sufficient grafting density. Binary brushes constituted from two incompatible polymers can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physicochemical surface characteristics as wettability, surface charge, chemical composition or morphology, and furthermore to create responsive surface properties. It is also possible to fix surface structures obtained in this way by (photo)crosslinking of the layers. Mixed brushes of oppositely charged polyelectrolytes are representing a special case of responding surfaces, which are sensitive to changes of the pH in aqueous environment. It is shown that structural changes occur in the plateau region of the adsorption isotherm of a model protein and that changes of the pH also cause changes in the structure of the adsorbed protein layer.

Equilibrium swelling and mesoscopic structure of a diblock copolymer gel in a selective solvent

Our previous analytic model [A.I. Victorov, C.J. Radke, J.M. Prausnitz. Molec. Phys., 100, 2277 (2002)] of a block-copolymer gel swollen in selective solvent was obtained from self–consistent field theory in the strong–segregation approximation; it takes into account the structure of the gel on the mesoscopic scale but is restricted to the case where the solvent–selective polymer subchains are located in the inner (minority) domains. In this work, the model is generalized to include swollen outer domains. The dependence of the equilibrium microdomain size on solvent uptake has been established. We calculate equilibrium swelling and determine relative stabilities for gels of different morphologies. Predicted equilibrium profiles of polymer segments are compared with computer simulation. Based on the average–solvent–fraction approximation, results obtained for an athermal solvent are very close to those from equilibrium profiles. Attention is given to the effect of partial restrictions in self–assembly of polymer chains on microdomain spacing and on equilibrium swelling.

Novel polymers: Molecular to nanoscale order in three dimensions

The assembly of polymer chains in solution is a powerful method that is leading to the preparation of interesting and unique macromolecular-based synthetic nanostructures. Specific control over the intramolecular and intermolecular physical interactions dictates either the folding of single chains or the aggregation and ordering of multiple chains. This control is provided through the selective placement of functional groups along the polymer backbone and the relative strengths of their attractive and repulsive interactions.

Pressure-Sensitive Microvalves Made from Polymer Brushes

AbstractWe describe a novel microvalve, constructed from polymer chains end-grafted onto opposing surfaces of a narrow slit. The assembly of polymer chains acts as both sensor and valve for microflow control and bypasses the need to construct an external feedback mechanism. This microflow control results from densely grafted chains which repel one another and stretch away from the surface, forming a brush which acts as an elastic and impenetrable layer. The height of a sheared brush increases or decreases depending upon solvent quality, i.e the layer can show a negative Poission's ratio. The discharge through the brushlined conduit is a non-linear function of pressure enabling different modes of valve operation. For brushes which extend moderately into the inter-slit region the valve assembly maintains constant discharge over a wide range of pressure. For brushes which extend far into the inter-slit region the valve assembly cuts off flow above a critical pressure, limiting the maximum discharge.

Morphology and deformation mechanisms of crystalline polymers

AbstractCrystalline polymers consist of regions of varying order ranging from perfectly crystalline to random and rubber‐like assemblies of polymer chains. Such structures may thus be represented in terms of statistical parameters characterizing the size and shape of ordered regions, degree of order and orientation of these regions. These parameters may be characterized by such techniques as x‐ray and light scattering. A study of the deformation of such polymers requires the specification of the change in these descriptive parameters with time, temperature, and morphology. The application of a number of optical techniques to this determination is discussed and typical results are presented. A deformation mechanism for crystalline polymers is proposed which is consistent with these observations.