Multicomponent Polymer Systems Research Articles

Surface modification strategies for multicomponent polymer systems, part I: Use of diblock copolymers as surface modifiers of rutile

Various functional diblock copolymers have been used as surface modifiers for rutile pigment in an effort to condition the solid for eventual use in multicomponent polymer systems. Coated surfaces were analyzed by inverse gas chromatography at infinite and finite dilution of the vapor phase, and by XPS. At high coverages (about 10% by weight of the pigment), the diblocks were randomly oriented at the air interface, effectively masking the surface of the rutile. At low diblock concentrations acid/base interactions dominated the orientation of the adsorbed molecule at the rutile interface, thereby also affecting the orientational states at the air interface. In this condition, the performance of the pigment in specified host polymer systems may be expected to vary with the selection of the diblock copolymer modifier. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1793–1805, 1997

Nanoscale Indentation of Polymer Systems Using the Atomic Force Microscope

The use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation and would be ideal for the evaluation of multi-component polymer systems, such as adhesives and composites. In this paper, previous work related to the development of the AFM as a nanoindentation device is reviewed, and a technique is proposed which allows the AFM to be used to probe local stiffness changes in polymer systems. Cantilever probes with spring constants ranging from 0.4–150 N m were used to investigate a number of polymer systems, including an elastomer, several polyurethane systems, thermally cured epoxies, a thermoplastic polymer-thermosetting polymer adhesive system, and a thermoplastic matrix composite.

Surface molecular mobility for copolymers having perfluorooctyl and/or polyether side chains via dynamic contact angle

It is well known that a segment of a multicomponent polymeric system such as copolymer selectively adsorb and orient to the surface of the system so as to minimize interfacial free energy in response to an environmental media. Surface molecular mobility of perfluorooctyl (PFO) group of acrylic copolymers, having PFO as a side chain, was investigated via dynamic contact angle and X.p.s. For all copolymers, more fluorine was detected than calculated amount from composition via X.p.s. In addition, the shallower sampling depth of X.p.s., the more fluorine was detected. These sample polymers exhibited a relatively large contact angle hysteresis. Advancing contact angle θ A for copolymers increased with an increase in PFO content. Receding contact angles were largely influenced by polar group of copolymers.

Scattering properties of multicomponent polymer solutions: polyelectrolytes, homopolymer mixtures and diblock copolymer

AbstractThis article reviews the understanding of static and dynamic scattering properties of multicomponent polymer systems in solution achieved during the past decade. We shall describe particularly ternary polymer systems which include polyelectrolyte solutions (polyion/counter‐ions/water), mixture of homopolymers (A and B)/solvent and the case of diblock copolymer (A‐B, linear or cyclic) solutions. The purpose of this paper is not an extensive survey of theoretical and experimental results obtained on the scattering behavior of these systems but rather an updating of recent results. For polyelectrolyte systems we shall focus, by means of scattering techniques, on the conformation of the polyelectrolyte chain and on the structure of the system induced by the dominant electrostatic interactions in solution involving polyions, counter‐ions and solvent. As for the mixture of homopolymers in solution and diblock copolymer/solvent systems, we shall mainly discuss their dynamic behavior and show that using linear response theory and the Random Phase Approximation (RPA), two relaxation modes describe the autocorrelation functions as revealed using dynamic light scattering (DLS) or/and Neutron Spin Echo (NSE) techniques: the first mode characterizes the concentration fluctuations and the second one the composition fluctuations. We shall discuss the scattering properties of these systems on the basis of recent developments with emphasis on possible coiling of the polyelectrolyte chain at low charge density and also how important parameters such as the mobility of the chain (diffusion process) and the interaction parameter (compatibility), which control the dynamics and the thermodynamics in homopolymer mixtures and diblock copolymer systems, could be deduced from scattering experiments.

Reactive Blending Methodologies for Biopol

Multicomponent polymeric systems containing Biopol as one of the phases are described as obtained according to two different procedures : radical polymerization of an acrylic polymer in the presence of Biopol, and melt-mixing of Biopol with polycaprolactone in the presence of peroxide. The decomposition of peroxide causes, in both cases, the formation of intergrafted species responsible for interfacial activity and compatibilization. The results of chemical, chemical-physical, morphological and mechanical tests, confirming the occurrence of such interactions, are reported.

Matrix Polycondensation: A New Route to Multicomponent Polymer System with Designed Properties

Abstract The regularities of polyesterification in the presence of a filler as a heterogeneous matrix were considered. The filler introduced into the reaction system before polycondensation process influenced not only the reaction kinetics but also the resulting properties of polymer composites produced. The composites obtained by polymer synthesis in the presence of the filler have higher mechanical, thermal, frictional and electrical properties as compared with those of the composites prepared by mechanical filling.

Characterization of Interphase Regions Using Atomic Force Microscopy

ABSTRACTThe use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation. In this paper, a novel technique is used to probe local property changes in multi-component polymer systems. Changes in indentation response in interphase regions are investigated for an adhesive system involving a diffuse polymer-polymer bond and for two composite systems. To date, diamond-tipped probes with effective spring constants of 150 and 310 N/m have been used to investigate polyimide and epoxy resin matrices reinforced by carbon fibers.

Polymer Surfaces and Interfaces

Since their commercialization in the late 1940s, applications for synthetic polymers have grown at an extraordinary rate, to the point where polymers are now ubiquitous in our society. The demands placed upon polymer performance have paralleled the growth in applications and has driven the development of sophisticated multiconstituent polymer formulations with many outstanding physical and mechanical properties. Many applications require that a polymeric material be attached to or in contact with another material. In some cases, such as the classic nonstick fry pan, as well as lubrication and release paper, it is desirable to create surfaces that do not interact with the material in contact. On the other hand, in applications such as rubber toughening of blends, filled or fiber-reinforced polymers, and coatings, dissimilar materials must adhere to each other if high performance is to be obtained. While the majority of the research and development efforts to date have centered on optimizing bulk properties, the focus is now shifting toward the development of polymer systems with controlled surface and interfacial properties.The recent flurry of activity in polymer interfacial science can be traced to the simultaneous emergence of three factors: a strong commercial need to control the surface properties of advanced multicomponent polymer systems, the availability of sophisticated theoretical methods for studying polymer surface and interphase problems, and the devel opment of new characterization techniques capable of investigating molecular level structure at polymer interphases. The seven articles that comprise this issue provide an overview of basic polymer interface science by discussing some of the current advances in polymer interface theory, by presenting many of the new techniques available for polymer interphase characterization, and by illustrating some of the interesting and challenging problems associated with their applications.

多成分系高分子の動的接触角及び湿潤張力の緩和現象

It is well known that a segment of a multicomponent polymeric system such as copolymers selectively adsorbs and orients to the surface of the system so as to minimize interfacial free energy in response to an environmental medium. Recently, a surface molecular mobility of a multicomponent polymeric system has been investigated via dynamic contact angle (DCA) and adhesion tension (γL cosθ=γS -γSL) relaxation (ATR). These methods are useful tools to investigate these phenomena because a reorientation of surface segments directly reflect to contact angle hysteresis when a polymer is moved into a different medium. We1-6) have already reported several papers on this behavior. Here we reviewed these papers.An interesting behavior was found for methoxypolyethyleneglycol methacrylate (MPEGMA) and methylmethacrylate (MMA) copolymers that the advancing contact angles in the second cycle of DCA were larger than that in the first cycle for these copolymers containing 30-70 wt% of MPEGMA. These behavior was explained by the molecular mobility and crystallization of PEG side chains.For poly (vinylalkylate) s (PVAI), advancing contact angle initially increased with an increase in the side chain length and after maximum at C 10, it decreased, while receding contact angle showed a complex behavior. A large contact angle hysteresis was observed. DCA also depend on the dipping velocity. The large relaxations of adhesion tension for PVAls with side chains from C 6 to C 10 were observed. From these result, it was shown that the surface molecule of these PVAls had the large molecular mobility. Reproducibility of ATR also was observed.DCA and ATR for methacrylate terpolymers having both hydrophobic polydimethylsiloxane (PDMS) and hydrophilic methoxypolyethyleneglycol (MPEG) side chains were measured. DCA for these terpolymers showed the different composition dependency depending on the length of both side chains. Large ATR also observed.

Interrelation between density functional and self-consistent-field formulations for inhomogeneous polymer systems

We provide a bridge between the density functional and self-consistent-field formulations for inhomogeneous polymer systems by deriving the self-consistent-field equations from a density functional approach. The density functional theory employs the zeroth-order inhomogeneous model of Gaussian chains in the presence of interacting interfaces (or more generally of chains whose single chain distribution functions are derivable from a diffusion equation). Nonideality is represented, for simplicity, using a random mixing model, and an implicit formal solution is used for the ideal free energy functional. Application of the standard density functional variational principle produces the self-consistent-field equations and provides a method for generating analytical approximations both to the density functional and to the self-consistent-field equations. The final density functional emerges in the form of a Landau-type expansion about an analytically tractable zeroth-order inhomogeneous reference system, and the important presence of chain connectivity contributions is quite evident. We illustrate the theory by analytically computing the leading contribution to the inhomogeneous density profile induced by the presence of a polymer–surface interaction in a polymer melt that is confined by an impenetrable surface. Future works will extend these analytical computations to treat surface segregation in multicomponent polymer systems with interacting impenetrable interfaces.

Molecular design of multicomponent polymer systems XIX: Stability of cocontinuous phase morphologies in low‐density polyethylene–polystyrene blends emulsified by block copolymers

AbstractPolyethylene–polystyrene blends containing small amounts of polyethylene (20 wt %) display a cocontinuous phase morphology that is very unstable in the absence of an emulsifier. The kinetics of coalescence at high temperature is therefore very sensitive to differences in the interfacial activity of added polymeric emulsifiers. The morphology of blends added with a pure or a tapered hydrogenated polybutadiene‐b‐polystyrene block copolymer is investigated as a function of annealing time at 180°C. Various image treatments (standard granulometry, opening size granulometry distribution, and multiscaling analysis) were used to quantify the morphological evolution of these blends. The results clearly demonstrate that the tapered block copolymer is definitely more efficient than the corresponding pure diblock for stabilizing the cocontinuous structure of these blends. The differential behavior is assumed to results from differences in the tendency of the two copolymers to segregate and form their own domains. © 1995 John Wiley & Sons, Inc.

Dynamics of Early Stage Spinodal Decomposition of Multicomponent Polymer Systems

The Cahn-Hilliard-Cook (CHC) theory with random phase approximation (RPA) for the time change in the structure factor in multicomponent polymer systems is used to describe the dynamics ofthe early stage spinodal decomposition. Explicit expressions on the time change in the structure factor for the block copolymer/homopolymer mixture have been obtained with the dynamics of microphase/macrophase separations of the mixture presented in detail

Compatibilization effect of a block copolymer in two random copolymer blends

The stability limit and spinodal points of a multicomponent polymer system have been studied with the structure factors, which were obtained using the random phase approximation and incompressibility constraint. Emphasis was placed on the effect of the volume fraction of component A, f I , in a block copolymer, A- block-B, on the spinodal points for macrophase separation of an (A- block-B)/(B- ran-C)/(A- ran-D) mixture. The behaviour of the spinodal point for macrophase separation, and thus the compatibilization effect, depends very much on f I for given weight fractions of the two homopolymers (or a homopolymer and a random copolymer). The spinodal points of microphase transitions in addition to those of macrophase separation are also discussed.

Liquid-Liquid Phase Separation in Multicomponent Polymer Systems. XXVI. Blends of Two Polydisperse Polymers

A method for computing phase diagrams of polydisperse A/B polymer blends is proposed, based on Flory-Huggins-Staverman thermodynamics, and employed to obtain cloud-point curves (CPCs), shadow curves, spinodals and coexistence curves for a series of systems. Often bimodal CPCs and shadow curves result, even for systems with a concentration-independent interaction parameter g. The importance of coexistence curves, as opposed to CPCs, for judging the A/B miscibility, recently observed in polydisperse blends, is confirmed in this study. Particular attention is here paid to the critical state. Analytical relations are derived for the critical point (CP) and the critical slopes of the CPC and shadow curve, as well as for the criterion of CP stability, all in terms of various molar-mass averages of A and B. The latter criterion then yields conditions for the existence of heterogeneous double CPs and triple CPs, important as markers announcing the proximity of a three-phase region. Interestingly, the sign of the critical CPC slope depends solely on the relative magnitude of the rz/rw ratios for the two polymers A and B. Hence, a CP located at the CPC's top should not be interpreted as a proof of both polymers' monodispersity. The validity of derived analytical relations is confirmed by numerically computed phase diagrams.

Polymer-polymer interactions

Abstract

THE FORMATION OF INTERPENETRATING POLYMER BLENDS

Formation of the thermoplastic blends of co-continuous morpholology has been discussed, the dynamic character of this process being stressed. Interpenetrating polymer blends represent the intermediate stage of a multicomponent polymer system during dispersive mixing. The time for reaching such a state of heterogeneity and its stability depend on the viscoelastic characteristics of the component polymers , their ratio in ablend, interfacial tension and mixing parameters. The role of particular factors influencing the formation of interpenetrating polymer blends has been presented for the LPDE/PS system. Because of the dynamic character of the evolution of polymer blend morphology upon mixing, the processing history specifications should accompany every morphology presentation

Single chain dynamics in a binary polymer blend

The dynamics of an individual chain in a binary polymer blend is investigated. A generalized Rouse equation takes into account the coupling to the dynamics of the surrounding polymer matrix. This generalizes Schweizer’s approach to a multicomponent polymer system. The results are applied to a symmetric binary blend. Emphasis is laid on the role of composition fluctuations, which are strongly enhanced close to the phase separation and then show critical slowing down. This has an impact on the dynamics of individual chains. As a result of the treatment, the internal chain motion is expected to be more strongly affected than the center-of-mass motion. A physical interpretation is presented such that the chains are strongly expelled from unfavorable environments. It is discussed how the results are modified if—instead of a mean-field treatment—the theory of critical phenomena is applied to describe composition fluctuations.

The role of thermal analysis in revealing the common molecular nature of transitions in polymers

A brief review of the authors' studies on the molecular nature of the β, α (glass) and “liquid—liquid” (II) transitions in flexible-chain polymers using different thermal analysis techniques is presented. DSC, far infrared spectroscopy versus temperature and dynamic mechanical analysis of statically loaded samples have been used. They enabled, for the first time, the common nature and fundamental interrelationship of the above-mentioned transitions in polymers of different structure to be established experimentally. It was found that the moving segment remained practically invariable over a wide temperature range, for temperatures T ≥ T β, and was close to the magnitude of the statistical (Kuhn) segment. Simple relationships between transitions parameters and main molecular characteristics of polymers have been found that offer a new approach for the prediction of transition characteristics, including the manifestation of the glass transition in multicomponent and plasticized polymeric systems, on the basis of the molecular parameters.

General formulation of the statistical mechanics of multicomponent polymer systems

AbstractThis paper summarizes different approaches to strongly interacting polymer systems. The first part of the paper discusses repulsive systems, i.e. polymers in a good solvent, polymer melts and blends. Corresponding field theories are reviewed and critically revisited from different points of view. The second part of the paper is devoted to attractive systems, i.e. polymers in a poor solvent, ionomers, polyelectrolytes under certain conditions, etc. New types to field theories have to be developed as theories for repulsive polymer systems no longer lead to the appropriate physics. The technical approaches used in the paper are field theory and path integrals. Novel possibilities for a microscopic theoretical description of these systems are reported.

Modified interpenetration function accounting for the excluded-volume effects in ternary polymer systems

The excluded-volume effect in polymer–mixed-solvent systems has been investigated in the light of the two-parameter theory. These multicomponent polymer systems exhibit some specific features quite different from polymer–single-solvent systems, involving ternary interactions and the synergic action of the mixed solvents at a given composition on polymer dimensions. Both effects are taken into account in order to derive a new expression for the interpenetration ternary function, ψT, and the expansion factor, αs, both being quantitatively evaluated for ternary systems based on polystyrene and poly(methyl methacrylate). In addition, a complementary treatment of the excluded-volume effects, proposed by Wolf, based on the evaluation of the intra- and inter-molecular interactions has been carried out.