Surfactant Surface-Patterned Starch Particles for Adsorption-Based Applications: The Role of Sabatier’s Principle

Abstract

This study reports on the structural characterization and physicochemical properties of surface modified starch particles (SPs). The surface of the SPs was patterned via controlled deposition of cetylpyridinium bromide (CPB) at the solid−solution interface with incremental CPB loadings, denoted as SP-CPBX, where X = 0.5, 2.5, or 5.0 mM CPB. The surface-patterned SPs were characterized by several complementary methods: spectroscopic (NMR, FT-IR, Raman, and SEM), thermoanalytical (DSC and TGA), powder X-ray diffraction (PXRD), gravimetric-based solvent swelling, zeta-potential (ζ), and particle size distribution (PSD). NMR spectral results reveal that CPB is bound at the starch−solvent interface via the pyridyl headgroup, whereas the tertiary structure of the SPs was maintained over the range of CPB doping, as revealed by SEM and PXRD results. The ζ-value results of the SP-CPBX systems reveal negative ζ-values at the starch surface, where tunable surface properties occur at variable levels of CPB surface patterning, as evidenced by the variable adsorptive affinity with water. Solvent swelling in water for the SP-CPBX systems reveal a dependence of the hydration properties on the level of CPB surface patterning, as highlighted by the unique physicochemical properties for the SP-CPB0.5 system, according to the relative accessibility of the active surface sites. The DSC/TGA and Raman/NMR spectral results of the SP-CPBX systems further support that variable surface coverage of CPB governs the interfacial adsorption of water according to Sabatier's principle. Furthermore, the SP-CPB0.5 system was compared among a variety of common bacterial strains for its antibacterial activity that met or exceeded the activity of SPs imbibed with conventional antibiotic agents. This study highlights that surfactant-modified starch is a sustainable material with unique adsorption properties that are switchable upon surfactant patterning. CPB-coated SPs possess improved antibacterial stability and functional versatility with potential utility as sustainable carrier systems for diverse applications that involve adsorption-based processes.

Water Vapor Adsorption–Desorption Behavior of Surfactant-Coated Starch Particles for Commercial Energy Wheels

“…As noted above, Karoyo et al 38 carried out a systematic study of the surface modification of starch particles (SPs) with CPB in an effort to determine the optimal level of monolayer surfactant doping (cf. Figure 9 in ref (35) or Figure 1 in ref (38)).…”

“…As noted above, Karoyo et al 38 carried out a systematic study of the surface modification of starch particles (SPs) with CPB in an effort to determine the optimal level of monolayer surfactant doping (cf. Figure 9 in ref (35) or Figure 1 in ref (38)). According to the trends in solvent swelling results in water, CPB-doped SPs revealed optimal swelling for surface-modified SPs at a loading concentration of 0.5 mM for the CPB surfactant (SP-CPB0.5).…”

“…The effect of the surface-bound CPB is to afford additional pores or hydrophile sites that enhance the vapor permeability of the CPB-coated starch, in line with the results for cassava starch coated with a nonionic surfactant reported by Brandelero et al 53 The minor differences in water vapor uptake capacity for the SP-CPB0.5 and SP-CPB5.0 systems may be related to compensation between CPB steric effects and the variable number of ion adsorption sites (HLB) character of the bound surfactant chains onto the surface of SPs. 38…”

“…38 The SP-CPB0.5 sample was chosen for this study based on its unique spherical morphology and optimum water uptake and swelling properties as characterized in the previous study. 38,39…”

“…By contrast, the longevity of SPs was improved for SP-CPB0.5, as evidenced by the enhanced antimicrobial activity of CPB toward a range of bacterial strains, as compared with unmodified SPs. 38 The aim of this paper is to further our research efforts toward new biopolymer desiccants 40−42 with improved sorption capacity, adsorption/desorption regeneration, and temporal stability by testing surfactant-coated SPs. Herein, SP-CPB0.5 (surfactant concentration = 0.5 mM) was selected based on a previous optimization study.…”