Controllable Morphology Transition Of Mesoporous Silica Induced By ?-CD

For the first time,vesicular and wormlike mesoporous silica with well-defined multilamellarstructureswerepreparedwithpositivelycharged didodecyldimethylammonium bromide?DDAB?/cetyltrimethylammonium bromide?CTAB?as structure-directing agents and?-cyclodextrin??-CD?as inducing agent,and tetraethylorthosilicate?TEOS?was used as silica source.Changes in the morphology of mesoporous silica were controlled by adding appropriate amounts of?-CD to the mixed DDAB/CTAB surfactant aqueous solution.The structural transition of the?-CD recognition-controlled phase in the mixed CTAB/DDAB surfactant aggregation was achieved.and a possible mechanism was preliminarily discussed.?-CD can selectively transfer the excess part of the major component?CTAB?from the aggregates to?-CD cavities,thereby resulting in aggregate changes of CTAB/DDAB.The added amount of?-CD can control multilamellar silica microstructures and induce a transformation from MLV to MLW then to MLV.When a small amount of?-CD?0.05 g?was added to the system,vesicular silica with six to seven layers was prepared.When the quality of?-CD increases to 0.1 g,a drastic change occurred in morphology from MLV to MLW.Almost all the MLV are converted into MLW.By further increasing the quality of?-CD to 0.15 g,the number of MLV conversely began to increase.Significant amounts of MLV with three to four layers coexisted with minor amounts of MLW with three to four layers.As the amount of?-CD continuously increased to 0.2⁰.25 g,the number of MLV increased until MLV dominated all the images.In other words,morphology transitioned from vesicular silica with six to seven layers to wormlike silica with three to four layers to vesicular silica with three to four layers.Based on the results,simple drug loading and release were performed with metformin hydrochloride as a model drug to assess and compare the storage capacity and in vitro release profiles of the mesoporous silica.Compared with parent MLS-n,the surface areas and the pore volume of MH-loaded MLS-n decreased,thereby indicating that MH was successfully loaded into the MLS-n voids.The MH loads on MLS-0.05,MLS-0.1,MLS-0.15,MLS-0.2,and MLS-0.25 are calculated with equation to have values of 29.1%,45.7%,42.1%,30.8%,and 40.6%,respectively.MLS-0.1 presented the highest drug loading capacity among the samples and MLS-0.05 showed the lowest drug loading capacity.In vitro studies have shown that MLS-0.05-MH shows a relatively steady release rate compared with the relatively rapid release rates of MLS-0.1-MH to MLS-0.25-MH.In order to evaluate the mechanism that controls the release kinetic process,the first order model was applied.For the first order kinetics model,good linear plots was obtained for MH released from MLS-n which the first order kinetics model fits well to the MH release.We take advantage of a dual-templating way by using sodium dodecyl sulfate SDS)/cetyltrimethylammonium bromide?CTAB?as structure directing agent,tetraethylorthosilicate?TEOS?was used as silica source and?-CD as inducing agent.The pH=9 phosphate buffer solution was used as the solvent.Mesoporous silica materials?tremella-like mesoporous silica and brush-like mesoporous silica?with different morphology were prepared by the classical hydrothermal synthesis method.By changing the amount of?-CD added,a transformation between mesoporous silica with different morphologies was achieved.A series of characterization of the prepared material was carried out,and the transformation from tremella-like mesoporous silica to brush-like mesoporous silica to remella-like mesoporous silica was observed.The synthesis of tremella-like silica having sizes ranging from 150 to 200 nm composed of as a result of the diameter of the U-shaped silica skeleton.Brush-like mesoporous silica fiber material is composed of a number of bundled fibers in an orderly manner,about6²0?m in length and about 180 to 220 nm in diameter.The mesoporous materials have surface areas ranged from 72.9¹06.5 m² g^-1 and pore volumes ranged from0.21⁰.35 cm³ g^-1.pH is a key factor in influencing SiO₂ morphology,pore structure and arrangement.We take advantage of a dual-templating way by SDS/CTAB as structure directing agent,?-CD as inducing agent.The pH=8 phosphate buffer solution was used as the solvent Mesoporous silica materials.Mesoporous silica materials with different morphology were prepared by the classical hydrothermal synthesis method.A series of characterization of the prepared material was carried out.The results show that the transformation from tremella-like mesoporous silica to brush-like mesoporous silica to tremella-like mesoporous silica was observed.But the size of the tremella-like SiO₂ is not uniform and the structure is irregular,and the size of it ranges from 70¹30 nm.Brush-like mesoporous silica fiber material is composed of a number of bundled fibers in a disordered manner,about 1¹0?m in length and about 180 to 220 nm in diameter.