Langmuir and Langmuir–Blodgett Films of Unsymmetrical and Fully Condensed Polyhedral Oligomeric Silsesquioxanes (POSS)

Abstract

The search for novel building blocks for preparation of nanostructures of unique properties is crucial for development of functional nanomaterials. Polyhedral oligomeric silsesquioxanes (POSS) may be regarded as organic–inorganic nanoparticles of unusual characteristics, i.e., monodisperse size, high temperature resistance, and small dielectric constant. Here, we study four derivatives of fully condensed polyhedral oligomeric octasilsesquioxanes. Seven corners of the POSS cages are substituted with isobutyl groups forming a hydrophobic tail, whereas the eighth substituent acts as a hydrophilic head due to a judiciously chosen functional group. Such design assures amphiphilic character of POSS molecules with well-defined hydrophilic head and hydrophobic tail. The combination of amphiphilicity, well-defined size and composition, and rheological properties of monolayers makes studied POSS interesting model for self-assembly, thin films, and interfacial investigations. The Langmuir–Blodgett technique is used as a method that provides the best control over the parameters of thin films formation. The functional hydrophilic group strongly influences the behavior of POSS at the air/water interface. The mercapto derivative, which seems most promising for preparation of complex nanostructures, appears to form aggregates and multilayer films. Three other studied derivatives (bearing glycerol unit, maleamic acid, and amino group) behave as classical amphiphiles at the air/water interface.

Synthesis of an Open‐Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

“…[25] In the case of OFP-POSS, the mosaics tructure of the monolayer produced at the air-water interface remained in the same form after the deposition of this filmo nto the solid substrate.T he presence of domains with oppositely directed OFP-POSS molecules, which are aligned at the surface, that is, direct contact of both the hydrophobic cores and the hydrophobic fluorinated groups with the molecules of wettingw ater resultsi nt he higher hydrophobicity of this layer than that of the PEG-POSS monolayer.M oreover,i ti sw orth mentioning that the measured value of the contact angle for the substrate modified by deposition of the OFP-POSS film is clearly lower (by about 208)i nc omparison with the wettability of the material modified by typical fluorinated polyhedraloligomeric silsesquioxanes (F-POSS). This result reflects the differences in the orientation of theset wo types of POSS molecules forming films on the solid substrate.…”

“…[25] In the case of the OFP-POSS monolayer,the rheological characteristics were consideredo nly for low surface pressurest hat is, 5a nd 10 mN m À1 ,d ue to its low value of collapse of approximately 11.8 mN m À1 .I ts hould be noted that the values of the elastic modulus E' determined for the OFP-POSS monolayer are higherw hen compared with the values of E' characterizing the PEG-POSSf ilm under the same conditions of study.T his may be due to astrongly hydrophobic nature of the OFP-POSS molecules formingamore insolublem onolayer in the LE phase at the air-water interface. Thus, althoughf or both OFP-POSS andP EG-POSSf ilms the viscoelastic response appeared, nevertheless these films have more elastic character.I nt he more compressed monolayer the stronger intermolecular interactions should exist, which is consistent with the results obtained.…”

“…[12,13] By using the process of hydrosilylation, it is possible to performf unctionalization with al arge group of organic derivatives ando btain silsesquioxanes with open-cage structures having three reactive groups.U nfortunately,t he open-literature reports on this subject are still very scarce and the most of the availablei nformation is contained in patents, which describe the way of the synthesis and the direction of applications. [22][23][24][25] However,i ti so bvious that the modification effect as well as the character of the monolayer formedb y POSS molecules strongly dependo nt he type of POSS compound. [14] The derivatives with 3-isocyanatepropyl groups can be used as cross-linking agents in bindersa nd hot-melta dhesives.…”

Kinetic and Binding Studies Reveal Cooperativity and Off‐Cycle Competition for H‐Bonding Catalysis with Silsesquioxane Silanols

“…Tri‐silanol‐containing POSS molecules (Figure , 1 a ‐ b ) contain seven silicon atoms in a “cube missing a corner” configuration (R 7 O 9 Si 7 (OH) 3 ) and have received interest due to their “hybrid properties”, possessing inorganic siloxane linkages (Si−O−Si), silanols (Si−OH), and organic groups (R) . In addition, recent applications of POSS‐triols include composites, nanostructures, and films …”

“…[16,17] In addition, recent applications of POSS-triols include composites, [18][19][20] nanostructures, [21,22] and films. [23,24] POSS-triols are considered to be established structural modelso ft he vicinal silanols present on silica surfaces based on their similars tructuralf eatures. [17,25] Homogeneous models for surfacesilanols present on silica and alumina have been derived from POSS-triol intermediates.…”