An innovative approach for covalent-bond-activated mechanoresponse by complexing rhodamine or spiropyran with cyclodextrin (CD) is reported. This approach endows diverse fl uorophores with perfect mechanochromism by introducing a supramolecular system. Unique characteristics such as noncovalent chemical modifi cation and convenient preparation make this approach promising for practical applications. The strong hydrogen bonds provided by CD play a crucial role in triggering the mechanochromic switch. First, the hydrogen bonds seize both sides of the fl uorophore's weak chemical bonds and tightly lock the fl uorophore in the cavity of CD. Second, the hydrogen bonds prompt the aggregation of complex inclusions in large ordered arrays and strengthen the molecular interactions. In this way, the weak chemical bonds can focus more external force and stretch more easily upon shearing (quantifi ed). This is the fi rst report of supramolecule-triggered mechanochromic switches. This study opens an avenue to correlate a mechanochemical reaction with a supramolecular system. [ 3 ] In recent years, the latter approach is appealing to more researchers due to the good color stability and signifi cant color transformation. [ 3d ] Reported achievements of the activation of mechanoresponsive molecules by covalent bonds can be summarized into two classifi cations. The fi rst is covalently modifying the molecules, especially with numerous hetero atoms, to facilitate the interactions such as hydrogen bonds, π-π stacking, and van der Waals force between molecules. These covalent chemical modifi cations require complicated syntheses. Moreover, although some molecules are elaborately modifi ed, a high (nonquantifi ed) external force is still needed to trigger the mechanochromic switches. [ 3d ] The second is the crystallization of solid molecules. [ 4 ] Without the need for chemical modifi cations, this approach is relatively convenient, but the crystallization of solid is constrained by numerous environmental and structural effects. A lot of effort will be taken in preparing the crystalline solid, thus complicating the strategy and limiting the application. Herein, we report an innovative approach for the covalentbond-activated mechanoresponsive molecules. The approach is characterized by noncovalent chemical modifi cation, low external force (0.7 kg for rhodamine-β cyclodextrin ( Rh-βCD ), 2.2 kg for spiropyran-β cyclodextrin ( SP-γ CD )) requirement, and convenient preparation. DOIMotivated by the previous fi ndings that CD can act as a host to interact with guest molecules, we introduce CD as a matrix in our mechanochromic research. CD is well-known for its capability of forming complex inclusions with small molecules. [ 5 ] The hydroxyl groups of CD form strong hydrogen bonds to induce host-guest interactions to stabilize the inclusion complex. [ 5c , 6 ] These excellent interactions are the basic elements for mechanochromism. These interactions, along with the easy strategy affording the inclusion, prompted us to use CD fo...
Dual pH-and light-responsive nanomicelles selfassembled from amphiphilic random poly(methacrylic acid-co-methyl methacrylate-co-7-(4-vinylbenzyloxyl)-4-methylcoumarin) (P(MAA-co-MMA-co-VM)) have been successfully prepared and employed as particulate emulsifiers to stabilize the oil/water interface. The selfassembling behavior of copolymers in a selective solvent is explored. The structural transitions of CP55 micelles based on a copolymer with 55 mol % hydrophilic methacrylic acid units are investigated by the dosage of ultraviolet irradiation and pH variation. As pH increases, the ionization of the carboxyl groups leads to the swelling of micelles. Both the size and polydispersity index of cross-linked micelles are far larger than those of un-cross-linked micelles under alkaline conditions. The comparison of the configuration of the un-cross-linked micelles and cross-linked micelles at the oil/water interface is investigated by scanning electron microscopy. The results show that the ability of swelling and conformational changing in response to external pH-and light-triggers largely affected the emulsifying performance of the particulate emulsifiers. Especially for emulsions stabilized by the cross-linked micelles, oil begins to separate out as pH elevated over 7.3 on account of the restricted conformational adjustment that resulted from the increasing interparticle cross-linking and electrostatic repulsion. The findings may be useful for challenging industrial areas where organic macromolecules and surfactants cooperate.
Dual-functional emulsifying/antifogging polymeric micelles have been prepared by the self-assembly of poly(2-(dimethylamino)ethyl methacrylate-co-methyl methacrylate-co-7-acryloxy-4-methylcoumarin) P(DMAEMA-co-MMA-co-AOM). On one hand, the polymeric micelles have spherical morphology and exhibit triple responsive behaviors. The sample with the DMAEMA/MMA/AOM molar ratio of 5/3/3 (T2) is chosen to investigate the influence of pH on the emulsifying performance, and the configuration of polymeric micelles on the oil/water interface is investigated. The amount of micelles arranged on the surface of solidified polymerized beads gradually decreases as the pH changes from 12 to 5, and then total phase separation and demulsification occur at pH 3. On the other hand, we prepare an effective antifogging coating by forming an interchain network (ICN) resulting from self-assembled micelles and photo-cross-linked coumarin units. The ICN-T2 coating can not only absorb water vapor rapidly but also avoid excessive swelling of the amphiphilic terpolymer, thus leading to excellent antifogging performance. To the best of our knowledge, the photo-cross-linkable coumarin derivative is first introduced into an antifogging polymer coating at the molecular level, successfully avoiding the use of chemical cross-linking agents. The coumarin-containing polymeric micelle may be applied in many industrial processes and will provide new insight into the interface or surface property of macromolecular materials.
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