Effect of grafted groups on adsorption conformation and adsorption behavior of guar gum: insights from molecular interactions

The adsorption conformation of guar gum molecules on silica surfaces determines the structural characteristics of the adsorption layer, potentially enabling diverse functionalities in engineering applications. However, the influence of grafted groups on the adsorption characteristics of guar gum remains unclear. The adsorption conformations and morphologies of unmodified ordinary guar gum (GG) and three modified guar gums — hydroxypropyl guar gum (HPG), carboxymethyl guar gum (CMG), and hydroxypropyl trimethylammonium chloride guar gum (HPTCG) — on silica surfaces were investigated via molecular dynamics simulations and AFM topography. The adsorption behavior of four guar gums was investigated by QCM-D experiment. The four guar gums exhibited distinct adsorption conformations: GG formed a mushroom-like structure, HPG adopted a “lying-flat” conformation with moderate folding, CMG presented an “L-shaped” orientation, and HPTCG displayed an upright conformation. AFM adhesion force measurements and chemical calculations indicated that the types and intensities of interactions between the four guar gums and silica surfaces varied. These differences result in different adsorption capacities, diffusion coefficients, adsorption layer stability, and layer structural characteristics of the four guar gums on silica surfaces. The results provide valuable insights for the molecular design of guar gum derivatives and their potential applications in interfacial fields.