Phase Behavior of Nonionic Polymer Hydroxypropylmethyl Cellulose: Effect of Gemini and Single-Chain Surfactants on the Energetics at the Cloud Point

Abstract

Nonionic cellulose ether−water systems have a characteristic feature of phase separation at certain temperatures, also termed the cloud point. The effect of various surfactants as additives on the phase behavior of nonionic cellulose ether, hydroxypropylmethyl cellulose (HPMC), has been studied. It was found that in the presence of ionic surfactants the cloud point (T CP) of HPMC decreased when small amounts of surfactant were added, and at higher concentration it increased. In the case of alkyltrimethylammonium bromides, surfactants with a longer alkyl chain (cetyltrimethylammonium bromide, CTAB, and tetradecyltrimethylammonium bromide, TTAB) influenced the T CP much more than that with a shorter alkyl chain (dodecyltrimethylammonium bromide, DTAB). Cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) were utilized to see the counterion effect on the T CP of polymer. Anionic surfactant sodium dodecyl sulfate (SDS) was found to be more effective as compared to its cationic counterpart with the same alkyl chain (DTAB), whereas nonionic surfactants showed no influence. From these observations it was concluded that the driving force was the interaction between the charged head groups of the surfactants and polar sites present in the nonionic HPMC. Gemini surfactants (α,ω-bis(hexa/tetradecyldimethylammonium)alkane dibromides) showed more influence on the T CP as compared to their conventional counterparts. The energetic parameters of clouding in HPMC in the presence of all surfactants used in the study were also calculated. Conventional surfactants had shown the contrast behavior of enthalpy and entropy changes at lower and higher concentration regions; i.e., ΔH c 0 and TΔS c 0 were positive at low concentration of surfactants but negative at higher surfactant concentrations. In the presence of gemini surfactants, both the enthalpy and entropy changes were always negative.

Thermodynamic Parameters of Anionic Surfactant‐Quaternary Phosphonium Bromides Systems at the Cloud Point

“…The first stage is enthalpy controlled, i.e., D s H°[ TD s S°, whereas the second stage is controlled by both enthalpy and entropy, i.e., D s H°& TD s S°. The nature and types of the additives added determine the values of enthalpies [24]. As mentioned earlier, the phosphonium counterion with phenyl rings is bulkier than its n-butyl counterpart.…”

Polymer-Amphiphile Interactions: An Overview

“…Effect of various additives (surfactants) on the phase behavior of nonionic cellulose ether, HPMC, was also studied [107]. Various factors, such as chain length, charge on the head group, counterion, etc., affected the CP of HPMC.…”

Comparison of the Composition and Structural Parameters of W/O Microemulsions Containing Gemini Imidazoliums with Those Containing Monomeric Analogues

“…In addition, GS had more influence on the TCP (temperature of cloud point) of the nonionic polymer cellulose ether. This might be due to the stronger interactions of GS as compared to their single-chain counterparts [24]. Recently, researchers showed that GS had more influence on the cloud point of amphiphilic drugs, and could serve as a better drug carriers [25][26][27].…”