Abstract:

This study systematically explores the molecular design advantages of succinic acid （SA） in hair conditioner systems and its pH-responsive characteristics, aiming to overcome the bottlenecks of traditional formulations, such as high lipid dependence and loose structure. Notably, the glutaric acid （GA） system, as another dicarboxylic acid, also demonstrates superior network properties, which collectively confirms the pivotal role of the dicarboxylic acid molecular architecture. Experimental results show that SA, through its dicarboxylic acid groups interacting with stearamidopropyl dimethylamine （SPA）, forms a pseudo-Gemini surfactant structure, thereby constructing a long-range ordered dense lamellar network. Under the condition of only 5% fatty alcohol, the static viscosity of this system （η₀=18 810 mPa·s） is significantly improved by 4.5 times compared to the lactic acid （LA） system. Additionally, the introduction of SA synergistically improves the wet combability （improvement rate of 67.51%）, antistatic properties （relative static voltage of 4.23%）, and anti-breakage performance （reducing hair breakage by 63% after 5 000 combing strokes）. Further investigation reveals that increasing the system pH from 4.5 to 6.5 promotes charge neutralization, optimizing the compactness of the lamellar network. This leads to a significant increase in zero-shear viscosity （η₀=35 940 mPa·s） and superior antistatic performance （relative static voltage of 1.48%）. Crucially, the consistent shear-thinning slope across the tested pH range ensures that dynamic spreadability remains uncompromised. This work elucidates a “static compactness-dynamic response” balance mechanism in conditioner systems and proposes a synergistic strategy combining molecular design with environmental parameter control to achieve simultaneous formulation simplification and performance enhancement. These findings provide a solid theoretical foundation and an innovative technical framework for developing high-performance hair conditioner products.

Key words: succinic acid, conditioner, pH-responsive, pseudo-Gemini surfactant, rheological properties, antistatic properties