Cycling conjugated polymers with different cations

Wang, Xuezheng; Smela, Elisabeth

doi:10.1117/12.658057

Cited by 6 publications

(6 citation statements)

References 16 publications

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“…The Cs + values, in contrast, drop rapidly towards zero, as if the Cs + ion moves much more slowly in the polymer, despite the smaller size of the non-hydrated ion. This apparent contradiction has also been observed in ion transport measurements in polypyrrole, where the largest, Li(H 2 O) x + ion, had the highest mobility [21]. We believe that the explanation for this apparent paradox is that the PPy film with inserted solvated water molecules (Li + and Na + ) is a quite different material than that with inserted non-solvated Cs + ions: the "naked" Cs + ion probably does not open the polymer up to the same degree as the solvated ions.…”

Section: Cation Effect On Strain As a Function Of Actuation Frequencymentioning

confidence: 79%

Speed and strain of polypyrrole actuators: dependence on cation hydration number

Jafeen

Careem

Skaarup

2009

Ionics

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Polypyrrole films have been characterized by simultaneous cyclic voltammetry driven force-displacement measurements. The aim was to clarify the role of cations in the electrolyte on the speed of response and on the strain of the film. The strain as a function of actuation frequency was studied in alkali metal chloride aqueous electrolytes. The intention was to test the hypothesis of the division of the inserted H 2 O molecules into categories: a smaller number strongly bound to the cation (corresponding to the inner solvation shell) and a larger number entering the film after the insertion of the cations because of forces related to osmotic pressure difference. The two processes have very different time constants: The solvated H 2 O molecules are associated directly with the cations, and are therefore inserted in a faster process, whereas the second type enters the film much more slowly. At higher frequencies, the strain depends almost exclusively on insertion of strongly solvated cations and therefore depends on the hydration number of the cations: Li + (hydration number~5.4) gives more strain than Na + (~4.4) and much more than Cs + (~0) as predicted by the model.

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Section: Cation Effect On Strain As a Function Of Actuation Frequencymentioning

confidence: 79%

Speed and strain of polypyrrole actuators: dependence on cation hydration number

Jafeen

Careem

Skaarup

2009

Ionics

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“…The latter conclusion is based on the observation that actuation strain depends on the (solvated) ion size. 79…”

Section: Discussionmentioning

confidence: 99%

Color and Volume Change in PPy(DBS)

Wang

Smela

2008

J. Phys. Chem. C

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The optical-mechanical-electrochemical coupling in polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), is studied during electrochemical switching. Cations enter this material during reduction, leading to an increase in volume. A special experimental geometry is used in which the top surface of the PPy film is covered by a transparent ion barrier, which constrains the charge-compensating cations to enter the film only at the edges. The cation concentration determines the volume of the polymer and is also directly related to the oxidation level of the polymer, which in turn determines its color. During electrochemical reduction, the edges of the film lighten, and this light color travels as a front to the center of the film. At the same time, the height of the film increases when and where the color lightens, and the increase in height is directly proportional to the change in color intensity. The height and the intensity attain their maximum values as the front passes and do not increase further thereafter, indicating that the ion concentration in the fully reduced state has a maximum value that is not exceeded. The color and volume changes are associated with only the first pair of peaks in the cyclic voltammogram, which represent only a fraction of the consumed charge in a typical electrochemical scan.

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“…Prior work on PPy(DBS) has shown that upon the first-ever reduction of the film, the out-of-plane volume increases approximately 60% as cations and water are pulled into polymer for the first time [28,31,51] (depending on the cation; these values are for Na + [52]). Upon re-oxidation, however, the film does not contract all the way back to its original thickness: there is a semi-permanent increase of ~25% due to ions and water that remain in the film.…”

Section: Discussionmentioning

confidence: 99%

Chronoamperometric Study of Conformational Relaxation in PPy(DBS)

West¹

2009

J. Phys. Chem. B

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In conjugated polymer devices that switch from one oxidation level to another, such as artificial muscles, it is important to understand memory effects that stem from conformational relaxation movements of the polymer chains. Chronoamperometry during electrochemical switching of polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), is used to gain insight into the conformational relaxation kinetics. During oxidation and reduction (stepping to the anodic and cathodic voltages, respectively), an exponentially decaying current is observed, but a shoulder appears during reduction when the cathodic voltage is high enough. Subtracting an exponential curve fit from the reduction current yields a small current peak at the shoulder position. The position of this peak depends logarithmically on the applied cathodic potential, the anodic potential that was applied just prior to the reduction step, and on the time that the prior anodic voltage was held. These results are consistent with the electrochemically stimulated conformational relaxation (ESCR) model. BackgroundIn this thesis, polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), a conducting polymer, was electrochemically studied in an attempt to quantify the conformational relaxation which occurs during reduction and oxidation. Conducting polymers, and PPy(DBS) in particular, are used in actuators, such as artificial muscles, because of their ability to change volume. Previous work by the research group of Dr. Toribio F. Otero (a co-author on the journal paper in preparation as a result of this work) has extensively characterized the conformational relaxation in some types of conjugated polymers, and a model (Electrochemically Stimulated Conformational Relaxation, or ESCR) has evolved as a result. However, the model has not yet been applied to PPy(DBS). Not including conformational relaxation, PPy(DBS) has been extensively studied and characterized by many groups, including that of Dr. Elisabeth Smela, a co-advisor in this work. Therefore, the motivation for this thesis was primarily to bridge the gap between the two research groups by characterizing the conformational relaxation that occurs in PPy(DBS). Conjugated PolymersA conjugated polymer (CP) is a polymer containing alternating single and double bonds between repeating units. This structure allow CPs to conduct electricity when an electron is removed from one of the double bonds; the missing electron, or "hole" can move along the polymer chain.By removing electrons, CPs become positively charged (oxidized); adding electrons renders them electrically neutral (reduced). This oxidation and reduction can be accomplished 2 electrochemically, when the polymer is in direct contact with a solid conducting electrode and a liquid electrolyte.The electrochemical switching of CPs between the oxidized and reduced states is accompanied by transport of ions in the electrolyte in order to maintain charge neutrality. I.e., upon oxidation, the net positive charge on the polymer is compensated by either cation egress ...

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Cycling conjugated polymers with different cations

Cited by 6 publications

References 16 publications

Speed and strain of polypyrrole actuators: dependence on cation hydration number

Speed and strain of polypyrrole actuators: dependence on cation hydration number

Color and Volume Change in PPy(DBS)

Chronoamperometric Study of Conformational Relaxation in PPy(DBS)

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