Polymer Concentration Profile Research Articles

Calcium alginate gel fibers: Influence of alginate source and gel structure on fiber strength

AbstractThe low‐deformation extension modulus was measured for Ca–alginate gel fibers prepared from alginates of different compositions and molecular weights. The modulus showed an increase with increasing molecular weight for alginates of the same composition and sequence parameters. Fibers prepared with an inhomogeneous polymer concentration profile showed higher moduli than did fibers with a homogeneous polymer concentration profile. The higher modulus observed for fiber prepared from an alginate with low Ca2+ affinity is tentatively explained as resulting from a higher degree of polymer chain alignment. © 1994 John Wiley & Sons, Inc.

Oxygen enrichment on polymer surfaces measured by heavy ion elastic recoil detection

Using 35Cl elastic recoil detection (ERD) analysis, oxygen enrichment was found on the surfaces of polystyrene and a random copolymer of styrene and acrylonitrile containing 38.7 wt% acrylonitrile. The samples were prepared in a hot press at 200°C between two silicon wafers in an air environment. The oxygen-rich layer on top of the samples was less than 20 nm thick. Heavy ion ERD seems to be a promising method to study the chemical composition of polymer surfaces and concentration profiles up to a depth of several hundred nanometres.

Gel Permeation Chromatography/Fourier Transform Infrared Interface for Polymer Analysis

A new solvent elimination interface capable of operating at elevated temperatures, here 145°C, has been used to collect polymer molecular weight fractions eluting from a gel permeation chromatogram and to prepare them for IR analysis. The sample is deposited continuously onto a rotating germanium disk which can subsequently be scanned with the use of GC/FT-IR software, allowing direct access to the polymer or copolymer composition as a function of molecular weight. Data are presented here for an ethylene-propylene copolymer which has a distinct bimodal molecular weight distribution. Both the concentration profile and the “composition distribution” are examined. For the polymer concentration profile, comparison is made between the chromatogram obtained with a differential refractive index (DRI) detector and the IR detector (plotting the absorbance as a function of time using Gram-Schmidt vector orthogonalization). The copolymer composition is determined from the relative absorbance of methyl and methylene groups in the CH stretching region. The results show a small change in propylene content as a function of molecular weight, and there is good agreement between composition calculated with the use of the Gram-Schmidt and point-to-point methods.

Chemical grafting of silane end-functionalized polymer on silicon surfaces

AbstractX-ray and neutron reflectivity was used to determine the kinetics of adsorption and characterize the concentration profile of a low molecular weight trichlorosilane endfunctionalized polystyrene adsorbed onto polished silicon wafers. Higher adsorbed amounts were obtained from a cyclohexane solution of the polymer rather than toluene, with kinetics that followed a stretched exponential behavior. For moderately high grafting densities the polymer concentration profile in deuterated toluene (a good solvent) was best modelled using a small tailed parabola. In deuterated cyclohexane (a poor solvent) the brush profile steepened but was substantially smoother than a step, while in D20 (a non-solvent) it became step-like.

Structure of polymer layers adsorbed from concentrated solutions

We study by neutron scattering the interfacial strucuture of poly(dimethylsiloxane) layers irreversibly adsorbed from concentrated solutions or melts. We first measure the thickness h of the layers swollen by a good solvent as a function of the chain polymerisation index N and of the polymer volume fraction in the initial solution Φ. The relation h ≈N0.8Φ0.3, recently predicted from an analogy between irreversibly adsorbed layers and grafted polymer brushes, describes well our results. We can therefore deduce that there is at least one large loop of about N monomers per adsorbed chain. We also study the shape of the polymer concentration profile in the layers by measuring on two samples the polymer-solid partial structure factor, that is proportional to the Fourier transform of the profile. The model of pseudobrushes predicts a concentration decay varying with the distance of the wall z as z-2/5. This power law profile accounts quantitatively for the angular variation of the polymer-solid cross structure factor but it is difficult to distinguish it without anbiguity from less singular profiles. It implies that the adsorption of PDMS onto silica is sufficiently strong and fast to quench completely the loop distribution in the initial layer.

Velocity profile statistics in a turbulent boundary layer with slot-injected polymer

The modification of a flat-plate turbulent boundary layer resulting from the injection of drag-reducing polymer solutions through a narrow inclined slot into the near-wall region of the flow has been studied. Two-component coincident laser-Doppler velocity profile measurements were taken with a free-stream velocity of 4.5 m/s with polymer injection, water injection, and no injection. Polyethylene oxide solutions at concentrations of 500 and 1025 w.p.p.m. were injected. These data are complemented by polymer concentration profile measurements that were taken using a laser-induced-fluorescence technique. Also, integrated skin friction measurements were made with a drag balance for a range of polymer injection conditions and free-stream velocities. The immediate effects of polymer injection are a deceleration of the flow near the wall, a dramatic decrease of the vertical r.m.s. velocit}’ fluctuation levels and the Reynolds shear stress levels, and a mean velocity profile approaching Virk's asymptotic condition. These effects relax substantially with increasing stream wise distance from the injection slot and become similar to the effects observed for dilute homogeneous polymer flows.

On the adsorption of polymer solutions on random surfaces: the annealed case

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOn the adsorption of polymer solutions on random surfaces: the annealed caseDavid Andelman and Jean Francois JoannyCite this: Macromolecules 1991, 24, 22, 6040–6042Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://doi.org/10.1021/ma00022a022RIGHTS & PERMISSIONSArticle Views65Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (288 KB) Get e-Alerts Get e-Alerts

Interpretation of neutron reflectivity data of polymer concentration profiles at the liquid/air interface

Neutron reflectivity has been used to characterize the concentration profile of a linear flexible polymer adsorbed from good solvent at the liquid/air interface. Different models are considered in the interpretation of the reflectivity data. It is found that using the self-similar profile predicted by the scaling theory, the results obtained are consistent with those of surface tension measurements. The concentration profile obtained can be described as follows: in close proximity to the surface, there exists a monomer-rich zone, D, which is determined to be 10–15 Å thick and is independent of polymer molecular weight and of bulk concentration. Beyond D, the profile decreases with a self-similar structure with the manomer density scaling as φ( z) ∼ z − 4 3

Neutron reflectivity studies of polymer concentration profiles at the liquid/air interface

The concentration profiles of poly(dimethylsiloxane) adsorbed from toluene solutions are found to exhibit a self-similar structure as predicted by scaling theory; the results are consistent with surface tension data which support a strong adsorption and weak coupling case for the system studied. The monomer-rich zone and the concentration profile are independent of polymer molecular weight and bulk concentration

Observation of Polymer Concentration Profile by Neutron Reflection

Abstract Polymer solutions show remarkable effects near the free surface, reflecting the tendency for preferential adsorption of the component having the lower surface tension γ. For example, in the case of polydimethyl siloxane (γ p 20.6 mN/m) in solution in toluene (γ s = 28.5 mNm), the difference between solvent and solute surface tension is positive.1 The Polymer is adsorbed at the liquid-air interface. This strong adsorption leads to a concentration profile extending over several hundred Angstrμms. We present here the results of preliminary determinations of such a profile by neutron reflection.

Stability criteria for the design of graded polymer buffers

The graded polymer buffer technique is often used to minimize the amount of polymer to be injected during polymer flooding. A drawback of this method is the impairment of mobility control due to viscous instabilities within the polymer slug itself. This paper presents new criteria for the economic optimization of polymer usage, while preserving the effeciency of the mobility control. The numerical model takes into account dispersion and time-dependent effects in the polymer concentration profile. Stability domains are presented as function of the injection parameters, i.e., the flow rate and the rate of decrease of the polymer concentration. The method is illustrated for the case of Xanthan polymer flow in Berea sandstone.

Molecular weight dependence of polymer interfacial tension and concentration profile

Measurements of the interfacial tension γ between immiscible polymers of low molecular weight have not resolved the question of how γ depends on the degree of polymerization N. In this paper the issue is addressed theoretically by solving equations derived earlier, but previously solved only in the infinite molecular weight limit. The basic origin of molecular weight dependence is entropic adsorption of chain ends to the interfacial region. It is found that the interfacial tension and concentration profile across the interface approach the infinite degree of polymerization limit like N−1. No sign is found of the N−2/3 approach reported to fit the data, although not unambiguously. If correct, N−2/3 may be a law applicable over a limited range, and not asymptotically.

Polymer concentration profile near a liquid-solid interface: evanescent wave ellipsometry study

The phase retardation angle, ~~. as a function of the incident angle was measured to study adsorption and depletion of polymers near a solid substrate from a solution by use of an evanescent wave ellipsometry technique. A lightly sulfonated ionomer dissolved in a polar solvent displayed an appreciable interfacial adsorption layer, while the nonionic precursor in ethyl acetate exhibits a depleted concentration profile. The results are in good agreement with adsorption or depletion layer profiles obtained previously by other techniques, i.e., X-ray fluorescence for polymer adsorption and optical fluorescence evanesent wave technique for depletion.

Formation of membranes by means of immersion precipitation : Part I. A model to describe mass transfer during immersion precipitation

Equations and boundary conditions are derived for the isothermal diffusion processes in the coagulation bath and in the polymer solution after immersion of a cast (ternary) polymer solution into a (binary) coagulation bath. The mass transfer is expressed in terms of thermodynamic driving forces and frictional coefficients. The frictional coefficients in the ternary system are assumed to be interrelated through the Onsager reciprocal relations and to be related to the measurable frictional coefficients defined in the three limiting binary composition ranges. In combination with knowledge about the demixing processes which can take place in the polymer solution (liquid-liquid phase separation or solid-like aggregate formation), this model makes it possible to calculate the polymer concentration profile in the immersed film at the moment of demixing of the polymer solution as a function of several process parameters. The calculated concentration profile and its relation to the asymmetric structure of the ultimate membrane are presented in Part II 1 1 J. Membrane Sci., 34 (1987) 67. .

Experimental Studies of Polymer Concentration Profiles at Solid-Liquid and Liquid-Gas Interfaces by Optical and X-ray Evanescent Wave Techniques

Machine learning (ML) is transforming all areas of science. The complex and time-consuming calculations in molecular simulations are particularly suitable for an ML revolution and have already been profoundly affected by the application of existing ML ...Read More

Confinedrandom‐flightpolymerchainsinsolution: exclusion from micropores and distribution near barriers

AbstractThe statistical basis of the entropic repulsion of dissolved random‐flight polymer chains from impenetrable passive barriers is described. The application of these ideas to the partial exclusion of linear and branched polymer chains from micropores and to the polymer concentration profile near a barrier is reviewed with emphasis on the mean projection of the chain as a measure of the exclusion effect.

Macromolecules in nonhomogeneous flow fields: A general study for dumbbell model macromolecules

The hydrodynamics of bead-spring model macromolecules in nonhomogeneous flows has recently been worked out. By taking a non-infinite distance between the beads (relative to the bead size) into account a hydrodynamic driving force was found. In this paper we explore the kinetic theory consequence of that force and show that non-uniform (polymer) concentration profiles are to be expected in nonhomogeneous flows. The diffusion equation for a dilute polymer solution is derived from the continuity equation for the distribution function. Arguments, leading to a well-ordered pertubation expansion of the continuity equation are advanced and the zeroth order function of this hierarchy is studied for models with linear springs. Details for the channel flow system are worked out with special emphasis on the relation between the polymer concentration and the parameters of the system. Explicit results are presented for models with linear springs. It is shown that if the Oseen tensor is not preaveraged, inadmissible results emerge.

Inhomogeneous polymer solutions: Theory of the interfacial free energy and the composition profile near the consolute point

AbstractThe Flory–Huggins formulation of the combinatorial entropy, supplemented with residual free energy, is applied locally to obtain the interfacial free energy and the concentration profile of polymer in the interface between two demixed polymer solution phases. Two choices were investigated for the residual free energy: a “regular solution” formulation and an empirical formulation of Koningsveld for polystyrene in cyclohexane. Asymptotic, analytical solutions of the equations near the critical solution point and solutions obtained by numerical calculations are given as a function of temperature for several molecular weights. At temperatures farther below the critical temperature the equations have no solutions. The reason for this is not entirely clear. The local formulation of the free energy used here is an improved version of a previous one, which gave wrong results for asymmetric systems (polymer in a low molecular weight solvent). This newer version is consistent with our theory of critical opalescence and gives a relation between the interface “thickness” and the correlation range of the concentration fluctuations. The calculated correlation ranges were in good accord with those found experimentally by Debye, Chu, and Woerman. That the newer version of our equations for an interface gives no acceptable solutions at lower temperatures could be caused by a “collapse” of a diffuse to a sharp interface as suggested by Nose.