Control of morphology for energy dissipation in carbon nanotube forests Matthew W. Brenner • Veera M. Boddu • Ashok Kumar Received: 7 May 2014 / Accepted: 30 September 2014 / Published online: 12 October 2014 Ó Springer-Verlag Berlin Heidelberg (outside the USA) 2014 Abstract This study focuses on the effect of carbon precursor on the carbon nanotube (CNT) morphology and energy dissipation. Benzene, toluene, and m-xylene were used as carbon precursors for the synthesis of CNT forests following a chemical vapor deposition process. The results indicate that substituents on the benzene ring increase entanglement in the CNT forests. The absorbed energy was slightly greater for CNT forests synthesized using m-xylene than for toluene, but was much smaller for benzene. When compressed to a strain of 0.67, the toluene CNTs absorbed more energy than the m-xylene CNTs. The restitution was much higher for the forests synthesized with m-xylene than toluene while it further decreased for the forests made with benzene. A strong correlation is also observed between the average diameter of the CNTs and the number of methyl substituents on the benzene ring. The control of the entanglement of the CNT forests can potentially be used to design high energy absorbing composites for blast energy dissipation. 1 Introduction Carbon nanotubes were discovered by Iijima [1] in 1991 and have ever since attracted a great deal of attention due to their remarkable thermal, optical, electrical, and mechanical properties. They have found many potential applications [2] as chemical sensors [3], transistors [4, 5], field emitters [6], atomic force microscopy, and scanning tunneling microscopy probe tips [7, 8]. Their exceptional mechanical properties include a high elastic modulus and large buckling and fracture strains [9–11]. Due to their high mechanical strength and low density, they have been incorporated into composites to increase their mechanical strength [12–14]. There are many methods used to fabricate CNTs including chemical vapor deposition (CVD) [15, 16], plasma-enhanced CVD (PE-CVD) [17], arc discharge [18], laser ablation [19], and flame synthesis [20]. Each of these methods involves the diffusion of carbon into a catalyst material to produce a CNT. The CVD method is widely used as there is flexibility in choosing the process param- eters to produce high yields of CNT forests that are verti- cally aligned and of high quality. Numerous studies have demonstrated that by controlling the catalyst, substrate, temperature, pressure, and total carrier gas flow rate, CNTs of varying structure and strength can be produced [21]. The choice of carbon precursor on CNT properties has also been widely studied [22–25]. Many of these experiments have investigated the impact of various carbon precursors and their mixtures on structural and chemical properties of CNTs such as morphology, diameter, defect density, and yield, as well as the optimal process temperature, chemical species present during pyrolysis, and carbon source inter- actions with the catalyst. The compressibility, impact resistance, modulus, restitution, elasticity, and other mechanical properties of CNT forests are also of great interest and have been extensively studied [26–28]. How- ever, relatively few studies have investigated the correla- tion between the carbon precursor and the mechanical properties of CNT forest including energy dissipation. Here, we report a study on how the carbon source impacts the structure and the resulting mechanical properties of the CNT forest. Our focus here is on the gross mechanical properties of the self-assembled CNT forest and not on the M. W. Brenner Á V. M. Boddu (&) Á A. Kumar Environmental Process Branch, US Army Engineering Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL), Champaign, IL 61826-9005, USA e-mail: Veera.Boddu@usace.army.mil 123 Appl. Phys. A (2014) 117:1849–1857 DOI 10.1007/s00339-014-8812-6