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Isothermal titration calorimetry (ITC) is used for determining surfactant/polyelectrolyte binding parameters as well as the enthalpy, entropy and Gibbs free energy of surfactant adsorption. The analysis has shown that the surfactant/polyelectrolyte adsorption process must have no more than two dominant binding states in order to apply the indirect ITC method of binding isotherm determination.

Gel-like coacervates that adhereto both hydrophilic and hydrophobicsubstrates under water have recently been prepared by ionically cross-linkingpoly(allylamine) (PAH) with pyrophosphate (PPi) and tripolyphosphate(TPP). Among the many advantages of these underwater adhesives (whichinclude their simple preparation and low cost) is their ability todissolve on demand when exposed to high or low pH. To further analyzetheir stimulus-responsive properties, we have investigated the pHand ionic strength effects on the formation, rheology and adhesionof PAH/PPi and PAH/TPP complexes. The ionic cross-linker concentrationsneeded to form these adhesives decreased with increasing pH and ionicstrength (although the complexes ceased to form when the parent solutionpH exceeded ca. 8.5; i.e., the effective pKaof PAH). Once formed, their ionic cross-links were most stable (asinferred from their relaxation times) at near-neutral or slightlyalkaline pH values (of roughly 6.5–9) and at low ionic strengths.The decrease in ionic cross-link stability within complexes preparedat other pH values and at elevated (150–300 mM) NaCl concentrationsdiminished both the strength and longevity of adhesion (although,under most conditions tested, the short-term tensile adhesion strengthsremained above 105Pa). Additionally, the sensitivity ofPAH/PPi and PAH/TPP complexes to ionic strength was demonstrated asa potential route to injectable adhesive design (where spontaneousadhesive formation was triggered via injection of low-viscosity, colloidalPAH/TPP dispersions into phosphate buffered saline). Thus, while thesensitivity of ionically cross-linked PAH networks to pH and ionicstrength can weaken their adhesion, it can also impart them with additionalfunctionality, such as minimally invasive, injectable delivery, andability to form and dissolve their bonds on demand. [ABSTRACT FROM AUTHOR]

Mixtures of polyelectrolytes andmultivalent counterions can self-assembleinto colloidal complexes. These complexes attract widespread interestin applications such as medicine, household product formulations,and separation processes. To facilitate the development of these colloidaldispersions, we examined isothermal titration calorimetry (ITC) asan automated screening tool for identifying the polymer and multivalentcounterion compositions that (1) form ionically cross-linked colloidalcomplexes and (2) lead to their rapid coagulation (and macroscopicphase separation). By studying various polyelectrolyte/multivalentcounterion mixtures, we have identified and generalized the featuresin the ITC data that indicate colloidal complex formation and coagulation.The limitations of this calorimetric screening method were also elucidated.These analyses suggest that ITC can be effective for screening theshort-term colloidal behavior of polyelectrolyte/multivalent counterionmixtures but are unreliable in revealing their long-term (equilibrium)properties. [ABSTRACT FROM AUTHOR]