The sol-gel transition of methylcellulose (MC) solutions in the presence of ortho-methoxycinnamic acid (OMCA) or cetyltrimethylammonium bromide (CTAB) and in the coexistence of OMCA and CTAB was determined by the rheological measurement. It has been found that the sol-gel transition temperature of MC solutions increases linearly with the concentration of either OMCA or CTAB in solution

respectively. However

in the coexistence of OMCA and CTAB

the sol-gel transition temperature of MC solutions remains invariable

independent of the concentration of CTAB in solution. The experimental results show that OMCA has priority to adsorb on the methyl group of MC chains to form polymer-bound aggregates. In particular

these aggregates inhibit the hydrophobic interaction between CTAB and the methyl group of MC chains completely. Taking into account the fact that OMCA is almost insoluble in MC-free solutions but dissolves very well in aqueous MC solutions

we propose the formation of the core-shell architecture prompted by OMCA and the methyl group of MC chains

with the methyl group of MC chains serving as the core and the self-assembly of OMCA molecules serving as the shell. Obviously

the formation of the core-shell structure increases the solubility of OMCA

improves the stability of methyl groups of MC chains at high temperatures and inhibits the hydrophobic interaction between CTAB and the methyl group of MC chains in solution. The abnormal behavior relating to the sol-gel transition of MC solutions in the presence of OMCA or in the coexistence of OMCA and CTAB is therefore explained. Upon UV irradiation

the sol-gel transition temperature of MC solutions in the presence of OMCA

or in the coexistence of OMCA and CTAB

decreases notably. However

the dependence of the sol-gel transition temperature of MC solutions as a function of OMCA concentration

or CTAB concentration in the presence of OMCA

does not change after UV irradiation.