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Simultaneously strong and tough ultrafine continuous nanofibers
Dimitry Papkov1, Yan Zou, Mohammad Nahid Andalib
1Department of Mechanical and Materials Engineering, Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0526, United States.
ACS Nano
|March 8, 2013
Summary
Ultra-fine polymer nanofibers exhibit remarkable improvements in strength, modulus, and toughness, challenging traditional material trade-offs. This discovery opens new avenues for advanced materials in critical applications.
Area of Science:
- Materials Science
- Polymer Science
- Nanotechnology
Background:
- Traditional materials science posits a trade-off between material strength and toughness.
- Previous studies showed improved modulus and strength in electrospun polymer nanofibers with decreasing diameter.
- Nanofiber toughness was expected to decrease with diameter reduction based on classical material property trade-offs.
Purpose of the Study:
- To investigate the effect of diameter reduction on the toughness of polyacrylonitrile (PAN) nanofibers.
- To analyze the mechanical properties (modulus, strength, toughness) of individual PAN nanofibers across a range of diameters.
- To understand the underlying mechanisms responsible for observed mechanical property changes in nanofibers.
Main Methods:
- Comprehensive mechanical analysis of individual, long (5-10 mm) polyacrylonitrile nanofibers.
- Systematic reduction of fiber diameter from 2.8 μm down to approximately 100 nm.
- Structural investigations and comparison with annealed nanofibers to correlate structure with mechanical behavior.
Main Results:
- Simultaneous increases in elastic modulus (0.36 to 48 GPa), true strength (15 to 1750 MPa), and toughness (0.25 to 605 MPa) were observed with decreasing nanofiber diameter.
- The most significant improvements were recorded for ultrafine nanofibers smaller than 250 nm, with no sign of saturation.
- Ultrahigh ductility (average failure strain > 50%) and toughness were attributed to low nanofiber crystallinity resulting from rapid solidification of ultrafine electrospun jets.
Conclusions:
- Nanofiber diameter reduction leads to simultaneous improvements in modulus, strength, and toughness, defying classical material trade-offs.
- Low nanofiber crystallinity, a result of rapid jet solidification, is the key mechanism for achieving superior mechanical performance.
- These findings challenge the long-standing paradigm favoring high polymer crystallinity for high-performance fibers and suggest broad implications for fiber science and technology, enabling advanced composites for safety-critical applications.
