Polymer Gel Systems Research Articles

Influence of a zwitterionic surfactant on the chromogenic behavior of a dye‐containing aqueous PVA–polyether gel network

AbstractThe effect of the addition of a zwitterionic sulfobetaine to a dye‐containing polymer gel composed of two polymers – poly(vinyl alcohol) (PVA) and polyether – was investigated. With increasing sulfobetaine content a remarkable reduction of the UV‐vis‐absorption intensity of the longest wavelength absorption band of Phenol Red in the aqueous polymer network was observed, even for sulfobetaine concentrations below its critical micelle concentration (cmc). It can be assumed that this effect is based on the formation of ionic complexes between dye molecules and either single sulfobetaine molecules or aggregates of sulfobetaine. Furthermore, thermotropic behavior occurs in the investigated polymer gel system even at a polyether concentration as low as 0.8 wt%. Copyright © 2003 John Wiley & Sons, Ltd.

Mode-coupling theory and polynomial fitting functions: A complex-plane representation of dielectric data on polymers

Recently, it has been shown that the higher-order A3 and A4 scenarios of the mode-coupling theory (MCT) are in many cases capable of providing a good description of the complicated dielectric spectra often encountered in polymeric systems. In this paper, more data from dielectric measurements on poly(ethylene terephthalate), poly(vinylidene fluoride), Nylon-66, poly(chlorotrifluoroethylene) (PCTFE), and the polymer gel system poly(acrylonitrile)-ethylene carbonate-propylene carbonate are evaluated within the A4 scenario of the MCT. For all these systems, very good agreement is found between the theoretical and experimental spectra. The data analysis is demonstrated to be facilitated considerably by plotting the data in the complex plane whereby the elliptic functions derived from the theory for the frequency-dependent dielectric function can be replaced by polynomials. For PCTFE, the scaling behavior predicted by the MCT could be verified and the temperature dependences of the extracted scaling parameters were found to be consistent with theory.

Transition Enthalpy for a Poly(N-isopropylacrylamide) Based Polymer Gel Estimated from the Clapeyron Equation

The applicability of the Clapeyron equation to the polymer gel system is demonstrated. It is shown that the stress dependence curve of the transition temperature of the gels undergoing the volume phase transition can be regarded as a phase boundary between swollen and collapsed phases. The enthalpy change at the volume phase transition is estimated from the Clapeyron equation for a poly(N-isopropylacrylamide) (PNIPA) based polymer gel. The transition enthalpy obtained by differential scanning calorimetry (DSC) measurements is estimated for a PNIPA based polymer gel and is compared with that obtained by the Clapeyron equation. It is shown that the transition enthalpy associated purely with the volume phase transition cannot be estimated by DSC while the Clapeyron equation gives the enthalpy change for the volume phase transition.

Investigation of swelling and diffusion in polymers by 1H NMR imaging: LCP networks and hydrogels

The kinetics of diffusion in polymers ranges from simple Fickian diffusion to higher-order diffusion, such as Case II diffusion. The conventional method for determining the characteristics of the diffusion of solvents into polymer matrices is by measuring the mass uptake of the polymer while the solvent penetrates the matrix. However, since such measurements perform observations at a macroscopic level, little information has been obtained relating to the properties of the solvent inside the polymer matrix and the mechanisms of the processes that control the diffusion. Nuclear magnetic resonance (NMR) imaging (MRI) is used to monitor the transport of solvents into solid systems in real-time. The method provides a one- or more-dimensional image of the density and the mobility of the solvent in a material. Furthermore, the mobility of network chains itself changes due to the softening influence of the solvent. The former (imaging of the solvent) can be used for a quantitative measurement of the diffusion coefficient whereas the observation of the network gives information about changes in the network properties (mobility, decrystallization) during the swelling process. The potential applicability of the NMR imaging techniques to polymer gel systems is demonstrated on the diffusion of organic solvents in polymeric materials like natural rubber, nematic-like networks, and hydogels.

In-situ self-assembling protein polymer gel systems for administration, delivery, and release of drugs

Sequential block copolymers consisting of tandem repetition of amino acids have been constructed and genetically produced based on the natural repeating structures of silk and elastin protein. Combinations of silklike and elastinlike amino acid sequence blocks in a high molecular weight protein polymer are used to confer properties similar to those observed with hard block and soft block segmented polyurethanes. A certain subset of these silk–elastinlike protein compositions, termed ProLastins, will undergo an irreversible solution to gel transition in physiological, aqueous solution. The transition occurs over time and can be controlled by temperature, solution conditions, and additives which either prevent or promote hydrogen bond-mediated chain crystallization. The process involves no covalent crosslinking. Characterization of the gelling properties of various ProLastin compositions and their ability to release compounds which are incorporated directly into the gels are presented.

Water Shutoff in the North Sea: Testing a New Polymer Gel System in the Heather Field, UKCS Block 2/5

Summary A new polymer gel system developed for high-temperature applications was successfully employed on Well H-43 of the Heather Field to isolate a high-rate water production zone. The high-temperature, organic polymer gel system has demonstrated long-term stability when mixed with seawater at temperatures as high as 350°F. Gel times can be delayed, allowing a large volume of polymer gelant to be placed. For Well H-43, 1,095 bbl of gelant were pumped through 1½-in. coiled tubing into a 15-ft layer of the Brent Group. The treatment increased oil production by 300 B/D and decreased water production by 2,290 B/D. A production log run 8 months later confirmed effective isolation, allowing the lower Brent to produce.

Raman spectroscopic study on water in polymer gels

Raman spectroscopic study on water in cross-linked polyacrylamide (PAAm) gels was carried out. The relative intensity of a peak corresponding to the collective mode of O-H stretching of water molecules in the polymer gels in comparison with that of free water significantly decreased with an increase in the degree of cross-linking. The relative intensity of the collective band in the solution of linear polyacrylamide was relatively-larger than that of the polymer gel system at the same concentration. The contribution of small water domains included in the polymer gel (so-called interstitial water) to the change in the Raman spectra was suggested

Dental soft polymers: plasticizer composition and leachability

The objective of this investigation was to identify the type and quantify the leachability of plasticizer constituents from dental soft polymer gel systems. The clinical implications are that some plasticizers are known to be potentially toxic and in addition, loss of plasticizer results in changes in physical properties of dental soft polymers. A total of 7 different constitutents were quantitatively identified in the 8 solutions analysed by GC and GC-MS. Specimens of gel material (plasticized polymer) were evaluated for loss of plasticizer while subjected to both static and cyclic tests (1 Hz, 5 min, ± 12 N) in H 2O at 37°C. With one exception, cycled specimens did not yield greater extraction of ester. The use of 1- 14C EtOH indicated complete diffusion of ethanol from the gel within 24 h. The data indicate that a typical denture soft lining would leach between 10–40 times the level of ester that would normally be obtained from food and the environment, but would leach about one-tenth of the most stringent ADI value.

In-Situ Gel Calculations in Complex Reservoir Systems Using a New Chemical Flood Simulator

SummaryThis paper presents results for a series of calculations on the deep emplacement of a polymer gel in a stratified reservoir model. These calculations were performed with a new chemical flooding simulator that has the facility to describe generalized chemical reactions between components. This code is described, and preliminary calculations on an in-situ gel treatment in a large model reservoir are presented. We find that to obtain significant amounts of incremental oil while avoiding very large pressure buildup, the polymer gel system must have the correct combination of long gelation times and good permeability-reducing properties in the high-permeability streak (residual resistance factor FR~ 10 to 40 in the cases studied here). No commercial polymer/ crosslinker systems are currently available that have the very long gel times required to obtain deep emplacement in a large reservoir system.

Influence of plasticizer on soft polymer gelation.

An evaluation has been made of the soft polymer gel systems of the type used as prosthodontic short-term denture-lining materials. The purpose of the study was to determine the effect upon gel strength and gelation time produced by variations in the composition of the plasticizer liquids. Poly(ethylmethacrylate) co-polymers were mixed with combinations of ethyl alcohol and the esters dibutyl phthalate (DBP), butylphthalyl butylglycolate (BPBG), and benzyl salicylate (BS). The relative rate of gelation of plasticizer polymer compositions was obtained by means of a reciprocating rheometer. The gelation rate was found to increase rapidly with an increase in the ethyl alcohol content. Significantly shorter gelation times were also found with liquids containing the lower-molecular-weight esters. A linear relationship was found between the ethyl alcohol content and the log of the gelation time. The higher-molecular-weight esters produced the strongest gel. A linear relationship was found between the gelation (log) times and the seven-day puncture strength. The ratio of polymer to plasticizer liquid was found to have a very significant influence upon the puncture strength and gelation time. Molecular weight or molecular volume of the ester plasticizers was found to have a greater influence on gel formation than the cohesive energy parameter. The strong polar bonding of ethyl alcohol was found to have a significant influence on both the rate of gel formation and the subsequent gel strength. The data indicate that controlled variations in the characteristics of plasticity and gel strength of dental soft polymer systems can be made to suit different clinical prosthodontic requirements.

The nitroglycerin polymer gel matrix system: a new method for administering nitroglycerin evaluated with plasma nitroglycerin levels.

A new topical dosage form of nitroglycerin has been developed in which nitroglycerin and its vehicle are incorporated in a polymer gel matrix of fixed dimension. Venous plasma nitroglycerin concentrations were measured for 24 h after application of nitroglycerin polymer gel systems measuring 10 cm and containing 2% nitroglycerin (wt/wt) to 10 normal male volunteers. Five of these subjects were subsequently tested with 20-cm2 gel systems of similar composition. With the 10-cm2 nitroglycerin polymer gel system, venous plasma nitroglycerin concentrations were 0.83 +/- 0.26 ng/ml ast 4 h and 0.89 +/- 0.23 ng/ml at 24 h. For the 20-cm2 system, venous plasma nitroglycerin concentrations were 1.83 +/- 0.55 ng/ml at 8 h and 1.81 +/- 0.13 ng/ml at 24 h. The only adverse effect noted was headache, which affected all the subjects tested with the 20-cm2 appliance. The plasma nitroglycerin concentrations obtained with the polymer gel system appear to be in a clinically useful range; thus this new form of topical nitroglycerin should be of benefit to patients in whom sustained plasma nitroglycerin concentrations are desirable, e.g., those patients with chronic congestive heart failure and angina on awakening.