Measurement of Forces between Hydroxypropylcellulose Polymers:  Temperature Favored Assembly and Salt Exclusion

Abstract

The thermodynamic forces between hydroxypropylcellulose (HPC) molecules at close separation have been measured using the osmotic stress method coupled with X-ray scattering. Two force regimes are apparent: a very short ranged, temperature insensitive force that dominates interactions within the last 2.5 Å separation and a longer-ranged force that varies exponentially vs distance with a decay length of about 3−4 Å. The longer-ranged force characteristics are strikingly similar to those found for many other macromolecules. We have previously argued that these characteristics are due to a hydration or water structuring force. The amplitude of the longer ranged force in these condensed arrays decreases linearly with temperature. The force switches from repulsive to attractive at ∼40 °C, about the same temperature at which HPC precipitates from dilute solution. The entropy of the HPC condensed array, derived from the temperature dependence of the force, also varies exponentially vs spacing with a 3−4 Å decay length. Measured forces are also surprisingly sensitive to added salt. Salt acts by its exclusion from the HPC phase. The salt concentration gradient within the space between polymers, inferred from the salt concentration dependence of the force curves, is itself apparently exponential with the about same 3−4 Å decay length as the force and entropy.

Assessing the Interaction of Urea and Protein-Stabilizing Osmolytes with the Nonpolar Surface of Hydroxypropylcellulose

“…Figure 4 shows the intensity of 90° scattered light as a function of temperature for dilute HPC (~100 µg/ml) in water and in 1 m proline. The midpoint transition without added osmolyte occurs at ~ 42 °C as has been observed by many others (13). Proline causes a significant decrease in the cloud-point temperature.…”

“…We have previously determined the transition entropy from the temperature dependence of forces between HPC polymers (13). ΔΓ w can be calculated by integrating equation (3).…”

“…We have previously determined the distance dependent entropy from the temperature dependence of the forces between HPC polymers in condensed arrays (13). The distance between polymers in the precipitate is assumed to be the same as the 13.9 Å spacing measured by x-ray scattering between polymers in ordered arrays at the 42 °C transition point between repulsion and attraction.…”

Miscibility Studies of Hydroxypropyl Cellulose/Poly(Ethylene Glycol) in Dilute Solutions and Solid State

“…By solution casting method these polymer blend films were also prepared and their miscibility studied using FTIR, DSC, X-RD, and SEM techniques. The compatibility of these polymer blends is discussed and it is concluded that the presence of hydrogen bonding groups [20,21] in these two polymers is responsible for the polymerpolymer interactions [22]. These results are presented here.…”

Long range interactions in nanoscale science

“…Figure 23 shows the ͑hypothetical͒ complexity of Nafion-like random copolymer membranes at atomic to macroscopic scales. Attempts to model structure and dynamics of such membranes at these scales have thus far met with limited success ͑Jang et al., 2004;Kreuer et al, 2004;Blake et al, 2005͒. The morphology assumed by uncharged diblock copolymers reflects, to a good approximation, only the volume fraction of the two components ͑Khandpur et Bates and Fredrickson, 1999͒. The excludedvolume and component-specific affinity effects of inorganic nanoparticles on diblock copolymer morphology, chemical and mechanical stability have been clearly demonstrated for the simpler case of nanoparticleguided self-assembly of uncharged block copolymers ͑Balazs et al, 2006͒.…”