Recent advances in thiophene-based molecular actuators

Abstract

A new class of molecular actuators where bulk actuation mechanisms such as ion intercalation are enhanced by controllable single molecule conformational rearrangements offers great promise to exhibit large active strains at moderate stresses. Initial activation of poly(quarterthiophene) based molecular muscles, for example, show active strains in the order of 20%. Molecular rearrangements in these conjugated polymers are believed to be driven by the formation of π-dimers (e.g. the tendency of π orbitals to align due to Pauli's exclusion principle) upon oxidation of the material creating thermodynamically stable molecular aggregates. Such thiophene based polymers, however, suffer from being brittle and difficult to handle. Polymer composites of the active polymer with a sulfated polymeric anion were therefore created and studied to increase the mechanical robustness of the films. This additional polyelectrolyte is a Sulfated Poly-β-Hydroxy Ether (S-PHE) designed to form a supporting elastic matrix for the new contractile compounds. Co-deposition of the polyanion with the conducting polymer material provides an elastic mechanical support to the relatively stiff conjugated polymer molecules, thus reducing film brittleness. The active properties of such poly(quarterthiophene)/S-PHE polymer actuator composites based on intrinsic molecular contractile units are presented and discussed.

Artificial Muscle Technology: Physical Principles and Naval Prospects

“…Upon oxidation the quarterthiophene groups have a stiong tendency to aggregate into a 7t-stacked structure. Simple inspection of the space-filling model in suggests that one dimensional changes as large of a factor of 9 are possible .for Poly(calixBBT) [71]. The proposed molecular actuation mechanism presented above and referred as 7t-dimerization or TI-TI stacking makes use of wavefimction overlap in 7i-conjugated polymers.…”

“…Features: These materials operate at low voltages (~ 2 V), and exhibit large strains (>20 %). They are expected to achieve high efficiencies and stresses [71]. Theory: Molecular conformational changes are induced in materials designed to utilize a variety of molecular mechanisms such as the cis-trans photoactivated transition, molecular bending in thianthrene or n-7t molecular dimerization [62][63][64][65].…”

Redox-responsive self-healing materials formed from host–guest polymers

“…Recently developed functional soft materials possessing switching, self-healing and self-repairing features are expected to have diverse applications (for example, in architectural materials and external coatings). Some research groups have attempted to create switching soft materials such as remotely actuated nanomaterials 10 11 12 13 14 , artificial molecular muscles 15 16 , drug-delivery systems 17 18 , biosensors and shape memory materials. Although there are previous examples of supramolecular hydrogels 19 where a sol−gel phase transition occurs using heat 20 , pH 21 , light 22 23 24 25 or redox 26 27 28 29 30 31 32 as a stimulus, it is difficult to create multi-functional soft materials owing to complicated designs and syntheses.…”

Biomedical Application of Electroactive Polymers in Electrochemical Sensors: A Review

“…Along with changes in conductivity, a changing oxidation state also results in changes in other properties, including volume, permeability, reactivity, solubility, optical properties, and thermoelectric properties. There are many excellent reviews covering CP optical properties [15,16], and thermoelectric properties [17] as well as CP applications in energy storage [18,19], photovoltaics [20,21], light emitting devices [22,23], sensors [24,25], and actuators [26,27]. The focus of this review is the use of CPs in electrochemical biomedical sensors.…”