Improving the Actuation Speed and Multi-Cyclic Actuation Characteristics of Silicone/Ethanol Soft Actuators

At a Glance

Metadata	Details
Publication Date	2020-07-28
Journal	Actuators
Authors	Boxi Xia, Aslan Miriyev, Cesar Trujillo, Neil Chen, Mark Cartolano
Institutions	Columbia University
Citations	31
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond-Enhanced Soft Actuators

Executive Summary

This research demonstrates the critical role of high-thermal-conductivity diamond fillers in enhancing the performance and reliability of thermally-driven soft actuators. The findings directly support the use of advanced CVD diamond materials, such as those provided by 6CCVD, for next-generation soft robotics and thermal management applications.

Performance Doubled: The addition of only 8 wt.% diamond nanoparticle filler reduced the actuation/de-actuation cycle duration by over 50% (from 402 s to 197 s).
Durability Increased: The maximal number of operation cycles increased significantly, from 40 cycles (unfilled) to 65 cycles (8 wt.% diamond filler), improving actuator reliability.
Thermal Management Validation: The slight increase in thermal conductivity (0.190 W/mK to 0.212 W/mK) was sufficient to alleviate thermal degradation and accelerate cooling, proving diamond’s efficacy in composite matrices.
Mechanical Integrity Maintained: The optimal 8 wt.% concentration achieved performance gains without compromising the critical mechanical properties (stress and modulus) required for soft robotics.
Data Reliability for AI: The improved multi-cyclic stability enabled the successful application of Long Short-Term Memory (LSTM) neural networks to accurately predict the actuator’s force-time behavior, paving the way for autonomous control systems.
6CCVD Advantage: 6CCVD supplies high-purity, high-thermal-conductivity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) materials, offering thermal performance far exceeding the nanoparticle grease used in this study (up to 2000 W/mK).

Technical Specifications

Parameter	Value	Unit	Context
Baseline Thermal Conductivity (0 wt.%)	0.190 ± 0.003	W/mK	Silicone/Ethanol Composite
Optimal Thermal Conductivity (8 wt.%)	0.212 ± 0.003	W/mK	With Diamond Nanoparticle Filler
Baseline Cycle Duration (0 wt.%)	402 ± 55	s	Actuation/De-actuation (First 30 cycles)
Optimal Cycle Duration (8 wt.%)	197 ± 18	s	Actuation/De-actuation (First 30 cycles)
Total Operation Cycles (0 wt.%)	40 ± 7	cycles	Maximal achieved durability
Total Operation Cycles (8 wt.%)	65 ± 2	cycles	Maximal achieved durability
Actuator Dimensions	25.4 mm (D) x 76.2 mm (H)	mm	Cylindrical Specimen
Actuation Force Target (F_max)	40	N	Upper bound force
De-Actuation Force Target (F_min)	10	N	Lower bound force
Heater Resistance	30	Ohm	Double-coiled 30 AWG Ni-Cr alloy wire
LSTM Prediction Error (Test RMSE)	1.8	N	8 wt.% specimen, same-specimen prediction
Cross-Specimen Prediction Error (Test RMSE)	2.7 ± 0.7	N	8 wt.% specimens, generalized prediction

Key Methodologies

The study focused on integrating diamond nanoparticle-based thermal filler into a platinum-catalyzed silicone/ethanol composite matrix (Ecoflex 00-35).

Composite Preparation: A mixture of 40 vol.% Ecoflex Part A, 40 vol.% Ecoflex Part B, and 20 vol.% ethanol was prepared. The diamond filler (MasterGel Maker Nano) was thoroughly mixed first with Part A, then Part B, for 30 s.
Specimen Casting: The mixture was poured into a 3D-printed Polylactic Acid (PLA) mold (76.2 mm long, 25.4 mm diameter).
Heater and Sensor Integration: A U-shaped 30 Ohm double-coiled Ni-Cr wire heater was centrally inserted. An NTC thermistor was inserted via a punched hole to measure internal temperature without touching the heater wire.
Thermal Testing: Thermal conductivity was assessed using a custom-built guarded hot plate device on specimens sealed in polyethylene bags to prevent ethanol evaporation.
Multi-Cyclic Actuation Testing: An automated testing unit was used to cycle the actuator between an upper force bound (F > 40 N) and a lower force bound (F ≤ 10 N) via Joule heating and passive ambient cooling.
Failure Criteria: Testing continued until the actuator temperature exceeded 145 °C or the heating time exceeded twice the initial cycle duration (indicating ethanol loss/matrix damage).
Machine Learning Implementation: Time-series data (force, internal temperature, ambient temperature, and PWM input) from the stable 8 wt.% actuator were used to train a Long Short-Term Memory (LSTM) recurrent neural network to predict future force output.

6CCVD Solutions & Capabilities

The research highlights the critical need for ultra-high thermal conductivity materials to manage heat dissipation in high-performance soft actuators. 6CCVD’s MPCVD diamond products are ideally suited to replicate and significantly extend this research.

Applicable Materials for Thermal Management

Research Requirement	6CCVD Material Recommendation	Thermal Advantage
High-Conductivity Filler	Thermal Grade PCD Wafers/Plates	PCD offers thermal conductivity typically >1000 W/mK, orders of magnitude higher than the 11 W/mK grease used, enabling superior heat spreading and faster cooling.
Integrated Heat Spreader	Optical Grade SCD Plates	SCD (up to 2000 W/mK) can be fabricated into thin, highly polished heat spreaders (down to 0.1 µm thickness) for direct integration beneath or around the heating element.
Advanced Composites	Custom Micronized Diamond Powder	While 6CCVD specializes in wafers, our high-purity CVD diamond can be processed into custom particle sizes for filler applications, ensuring maximum thermal transfer efficiency.

Customization Potential for Actuator Integration

6CCVD provides the necessary engineering and fabrication services to move this research from nanoparticle grease to robust, integrated diamond solutions:

Custom Dimensions: The paper used a 25.4 mm diameter actuator. 6CCVD routinely supplies PCD plates up to 125 mm and SCD plates up to 10 mm in custom thicknesses (0.1 µm to 500 µm), allowing for precise scaling and geometry matching for soft robotic components.
Precision Shaping: We offer laser cutting and etching services to create complex diamond geometries (e.g., micro-channels, specific heat sink shapes) for optimal thermal coupling within the silicone matrix.
Integrated Heating/Sensing: The study relied on external Ni-Cr wires and thermistors. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) to deposit thin-film heaters or sensor contact pads directly onto the diamond surface, creating a highly integrated, durable, and thermally efficient heating element.
Surface Finish: Our polishing capabilities (Ra < 1 nm for SCD, < 5 nm for PCD) ensure minimal surface defects, which is crucial for maximizing thermal contact area when bonding diamond heat spreaders to the soft polymer matrix.

Engineering Support

6CCVD’s in-house PhD team can assist researchers and engineers with material selection and design optimization for similar thermally-driven soft actuation projects. We specialize in tailoring diamond properties (e.g., nitrogen content, grain size, doping) to meet specific thermal, mechanical, or electrical requirements, ensuring the chosen CVD diamond solution maximizes actuation speed and multi-cyclic reliability.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The actuation of silicone/ethanol soft composite material-actuators is based on the phase change of ethanol upon heating, followed by the expansion of the whole composite, exhibiting high actuation stress and strain. However, the low thermal conductivity of silicone rubber hinders uniform heating throughout the material, creating overheated damaged areas in the silicone matrix and accelerating ethanol evaporation. This limits the actuation speed and the total number of operation cycles of these thermally-driven soft actuators. In this paper, we showed that adding 8 wt.% of diamond nanoparticle-based thermally conductive filler increases the thermal conductivity (from 0.190 W/mK to 0.212 W/mK), actuation speed and amount of operation cycles of silicone/ethanol actuators, while not affecting the mechanical properties. We performed multi-cyclic actuation tests and showed that the faster and longer operation of 8 wt.% filler material-actuators allows collecting enough reliable data for computational methods to model further actuation behavior. We successfully implemented a long short-term memory (LSTM) neural network model to predict the actuation force exerted in a uniform multi-cyclic actuation experiment. This work paves the way for a broader implementation of soft thermally-driven actuators in various robotic applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/act9030062

References

2015 - Design, fabrication and control of soft robots [Crossref]
2019 - A review of electro-stimulated gels and their applications: Present state and future perspectives [Crossref]
2017 - Liquid crystal elastomer actuators: Synthesis, alignment, and applications [Crossref]
2013 - A review of stimuli-responsive shape memory polymer composites [Crossref]
2019 - A multifunctional shape-morphing elastomer with liquid metal inclusions [Crossref]