# Temperature dependence of the near infrared absorption spectrum of single-wall carbon nanotubes dispersed by sodium dodecyl sulfate in aqueous solution: experiments and molecular dynamics study

Corey Valleroy, Rosa d'Ambrosio, Christophe Blanc, Éric Anglaret, Lucyna Firlej, Carlos Wexler

► To cite this version:

Corey Valleroy, Rosa d'Ambrosio, Christophe Blanc, Éric Anglaret, Lucyna Firlej, et al.. Temperature dependence of the near infrared absorption spectrum of single-wall carbon nanotubes dispersed by sodium dodecyl sulfate in aqueous solution: experiments and molecular dynamics study. Journal of Molecular Modeling, 2024, 30 (8), pp.286. 10.1007/s00894-024-06068-y. hal-04693471

HAL Id: hal-04693471

https://hal.science/hal-04693471v1

Submitted on 24 Mar 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>
# Shielding of Single Walled Carbon Nanotubes by Sodium Dodecyl Sulfate in Aqueous Solution: Molecular Dynamics Study

Corey Valleroy

crvrnp@mail.missouri.edu

University of Missouri

Carlos Wexler

University of Missouri

## Research Article

**Keywords:** single walled carbon nanotubes, adsorption, in situ sensors, molecular dynamics, surfactants

**Posted Date:** October 5th, 2023

**DOI:** https://doi.org/10.21203/rs.3.rs-3385823/v1

**License:** © This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License

**Additional Declarations:** No competing interests reported.

**Version of Record:** A version of this preprint was published at Journal of Molecular Modeling on July 27th, 2024. See the published version at https://doi.org/10.1007/s00894-024-06068-y.
# Shielding of Single Walled Carbon Nanotubes by Sodium Dodecyl Sulfate in Aqueous Solution: Molecular Dynamics Study

Corey Valleroy\*, and Carlos Wexler\*\*

Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA

\*e-mail: crvrnp@mail.missouri.edu

\*\*ORCID: 0000-0002-7038-2628

## Abstract

Single-walled carbon nanotubes (SWNT) exhibit a temperature dependent near infrared (NIR) exciton spectrum when solvated in water with the help of sodium dodecyl sulfate (SDS) surfactants. Since SWNTs are biocompatible and the NIR spectrum is in transparent window for biological tissue, this represents a potential means for sensing temperature inside cells. Here we seek to investigate a possible mechanism for this temperature dependence: changes in the water coverage of the SWNT as the surfactant structure changes with temperature. Using fully atomistic molecular dynamics simulations we observe for the conditions of our simulation that the SDS structure shield the SWNT effectively, with ~ 70% of water molecules removed from the first two adlayers; this coverage showing a modest temperature dependence. Although we are not able to directly show how this influences the NIR spectrum, this represents a possible pathway since there is a strong influence of the water environment on the excitons in SWNTs.

**Keywords:** single walled carbon nanotubes, adsorption, in situ sensors, molecular dynamics, surfactants

## 1. Introduction

Single-walled carbon nanotubes (SWNT) are quasi-1D materials that can be imagined by rolling graphene sheets into cylindrical tubes at a certain chiral angle with diameters $\lesssim$ 1 nm and lengths that are typically $\mu$m or more and which exhibit exceptional electrical, mechanical, chemical, and optical properties [1,2,3,4]. SWNTs have typically near infrared (NIR) spectra at wavelengths that are not heavily absorbed by biological tissue and fluids, which together with their small sizes and chemical inertness makes them ideal materials for *in situ* sensors in such systems [5,6,7,8]. Furthermore, the quasi-1D structure results in sharp peaks in the electronic density of states [9,10,11,12] and because SWNT are surface-only materials, the electronic properties are extremely sensitive to their chemical environment [6,7]. Here we focus on the application of SWNTs as possible temperature sensors [13].

Because the NIR optical transitions are excitonic with the electron-hole pairs at separations substantially larger than the SWNT diameter, they can be substantially modulated by the electric response of adsorbed layers [14,15,16]. In fact, for each *roll-up* vector (n, m) that defines the direction along which a graphene sheet is rolled to form a SWNT the variation of the optical signature with a particular environment is different [17] and peak shifts depend on the polarity of
solvents [18,19] and surfactants [17] used to help disperse the SWNTs [20,21,22]. Recent experiments have shown moderate temperature dependence of the NIR spectrum of SWNTs in aqueous environment [23]. D'Ambrosio et al. [24] observed changes in the 25-40 °C range of the NIR absorption spectra of SWNTs of several chiralities in aqueous solution in presence of excess sodium dodecyl sulfate (SDS) surfactants. SDS is a short linear amphiphilic molecule that was used to efficiently disperse and exfoliate the SWNTs [25,26].

Here we want to address a possible cause for the temperature dependence of the NIR spectrum of the SWNTs coated with SDS adlayers in aqueous solution. Given that neither the SWNT nor the water solution itself is expected to change significantly in the temperature range of the experiments [24], what is causing the change in the spectrum? Clues to the reasons have been exposed above: environmental influence on the excitons [14,15,16]. We hypothesize here that the very polar water molecules are the most substantial factor and that: (i) the SDS adlayer has the capacity to partially shield the SWNT from this influence, (ii) temperature-driven structural changes in the SDS adlayer modify the level of shielding.

In this paper we thus perform extensive fully atomistic molecular dynamics (MD) simulations of a SWNT covered by an SDS adlayer in water. We observe that for our configurations the SDS is able to shield the SWNT, excluding ca. 70% of water from the first two adlayers [22], but that the number of excluded water molecules is reduced as temperature increases. Although we are not able to directly show how this influences the exciton spectrum, our results represent a possible step towards elucidating the origin of the temperature dependence of the NIR spectrum [24].

## 2. Simulation Details

To perform the simulations, a (6, 5) SWNT containing 364 carbon atoms (1 period) was placed in the center of a ($L_x, L_y, L_z$) = (60 Å, 60 Å, 40.6 Å) periodic boundary condition box aligned with the z axis. The choice of the chiral *roll-up* vector ($n, m$) = (6, 5) was dictated by experimental results showing that these tubes exhibit the largest temperature-induced shifts in the NIR spectrum [24]. SDS molecules i.e., 26 dodecyl sulfate anions (42 atoms) and sodium cations were placed around the tube. To minimize the possibility of system getting trapped in unphysical or metastable states during simulations, the simulations were run starting from five different initial configurations with different arrangements of SDS molecules with respect to the SWNT (*alternating, screwed, parallel, alternating parallel, round*). Two of these configurations are shown on **Fig. 1**. All systems were then solvated with 3,955 water molecules.

MD simulations were performed in the (*N*, *P*, *T*) ensemble using the NAMD2 code [27] with a 1 fs time step. A *Langevin piston* Nosé-Hoover barostat was used with a target pressure of 101,325 Pa (1 atm), period of 100 fs and decay of 50 fs. A Langevin thermostat was used with a damping constant of 1 ps⁻¹. Each simulation consisted of an initial 100,000-step energy minimization followed by 18,000,000 steps (18 ns) of MD (at least 1 ns of additional system equilibration and up to 17 ns of production/averaging steps). Configurations were saved every 1,000 steps (1 ps).
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Initial configurations of the simulation: (a,b) *alternating*. (c-e) *screwed*. Other initial configurations not shown (*parallel*, *alternating parallel*, *round*) are variations of these two. Water molecules are excluded for clarity except for (e) where they are shown as blue O-H bond lines. SWNT is shown as gray bonds, SDS is composed of Na⁺ anion (blue) and dodecyl sulfate cation (H = gray, C = cyan, O = red, S = yellow).</figcaption></figure>

All interactions were modeled using the CHARMM force field [28], comprised of two-body bond stretching $V_b$, three-body angle deformation $V_a$, four-body dihedral angle deformation $V_d$, and nonbonded interactions $V_{nb}$ (electrostatic and Lennard-Jones). All interactions were reduced linearly to zero for distances in the 10 Å < $r_{ij}$ < 10 Å range and cut-off for $r_{ij}$ > 12 Å. To reduce simulation time, a neighbor list was kept for atoms within $r_{ij}$ < 14 Å and recalculated every 20 time steps. Particle mesh Ewald with a grid spacing of 1.0 Å⁻¹ was used to compute long-range electrostatic effects. The TIP3 model was used for water molecules [28]. More details about the interactions and parameters used are given in the **Appendix**.

**Figure 2** shows a typical configuration of the system after the energy minimization and equilibration. In absence of SDS water molecules form two reasonably structured layers on the nanotube sidewall despite its relative hydrophobicity [22], which increase the local polarity of the solvent [23]. The presence of SDS partially decreases this polarity effect by shielding the SWNT and forming an intermediate, relatively amorphous and very mobile film around it [17,29,30].
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Typical configuration at T = 300 K after ~ 12 ns of MD simulations. The surfactants partially cover the SWNT excluding water from the immediate neighborhood.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 3.** Evolution of the total energy and simulation box volume at T = 300 K for five different initial arrangements of SDS molecules with respect to the SWNT. Note the logarithmic scale of the time axes. Left panel: total energies. Right panel: simulation box volume. Fluctuations of E<sub>tot</sub> and V are later used to compute the system's specific heat and isothermal compressibility (Sec. 3.1).</figcaption></figure>

**Figure 3** shows the evolution of the simulation total energy and volume of the system at T = 300 K during MD simulations started from five different initial configurations described earlier. We observe first a sharp decline of the energy during the energy minimization (schematically represented by the 0-1 ps region), followed by an initial increase (i.e., turning on of kinetic energy), and rapid equilibration within < 0.5 ns. The system volume decreases initially by ~10% to account for voids left during the solvation procedure, equilibrating during the initial ~1 ns (the box dimension parallel to the SWNT axis is kept constant throughout the process). After the initial
equilibration, both the system volume, total energy, and all individual components of the potential energy (Eqs. (A1-A5), not shown), behave independently of the initial configuration. Simulations at T = 350 K (not shown) behave similarly as well.

We observed, however, long time scale variations in other observables (see **Sec. 3**); all averages computed henceforth were performed after equilibration for 2 ns (2 × 10⁶ steps) over various subintervals up to 2-18 ns (2 to 18 × 10⁶ steps).

# 3. Results and Discussion

## 3.1. Isothermal compressibility and specific heat

From the volume (V) and energy (E) fluctuations the isothermal compressibility $K_T$ and specific heat at constant pressure $C_p$ of the system may be calculated [31,32,33]:

$$K_T = \frac{1}{k_B T \langle V \rangle} \langle (V - \langle V \rangle)^2 \rangle, \qquad (1)$$

$$c_p = \frac{1}{N k_B T^2} \langle (E - \langle E \rangle)^2 \rangle, \qquad (2)$$

where $k_B$ is Boltzmann's constant and N is the number of molecules in the system. Given that there are 3,955 water molecules (11,865 atoms) vs. just 1 SWNT (364 atoms) and 26 SDS molecules (1,118 atoms) we expect that the system behavior will be close to that of pure water. **Table 1** shows excellent agreement for the specific heat for water. The compressibility of the system is higher than that of water, probably because of the significant exclusion of water molecules from the neighborhood of the SWNT due to the flexible SDS film (**Sec. 3.2**); it is also possible that the CHARMM [28] force field parameters are finely tuned for near physiological temperatures ~ 310 K, and less accurate at 350 K.

<table><caption>**Table 1:** Isothermal compressibility and specific heat at constant pressure.</caption><thead><tr><th rowspan="2">Runs</th><th colspan="2">300K</th><th colspan="2">350K</th></tr><tr><th>K<sub>T</sub> (1/Pa)</th><th>c<sub>p</sub> (J/mol K)</th><th>K<sub>T</sub> (1/Pa)</th><th>c<sub>p</sub> (J/mol K)</th></tr></thead><tbody><tr><td>Reference Value (water) [32,34]</td><td>4.51 × 10<sup>-10</sup></td><td>75.3</td><td>4.58 × 10<sup>-10</sup></td><td>75.6</td></tr><tr><td>Screwed</td><td>5.00 × 10<sup>-10</sup></td><td>76.9</td><td>6.45 × 10<sup>-10</sup></td><td>77.3</td></tr><tr><td>Round</td><td>5.05 × 10<sup>-10</sup></td><td>78.7</td><td>6.53 × 10<sup>-10</sup></td><td>77.2</td></tr><tr><td>Parallel</td><td>5.03 × 10<sup>-10</sup></td><td>78.0</td><td>6.57 × 10<sup>-10</sup></td><td>78.4</td></tr><tr><td>Antiparallel</td><td>5.00 × 10<sup>-10</sup></td><td>79.1</td><td>6.41 × 10<sup>-10</sup></td><td>78.1</td></tr><tr><td>Alternating</td><td>5.08 × 10<sup>-10</sup></td><td>80.7</td><td>6.41 × 10<sup>-10</sup></td><td>76.4</td></tr></tbody></table>

## 3.2. Shielding of the SWNT by the SDS adlayer

The formation of a (disordered) adlayer of SDS over the SWNT has the obvious consequence of partially shielding the nanotube from the very polar water molecules, thus likely modifying the exciton NIR spectrum as observed by D'Ambrosio [24]; **Figure 4ab** visually demonstrates this effect: (a) in absence of SDS molecules water forms adlayers at close vicinity with the SWNT (see also panel **4c**), consistent with Ref. [22]; (b) With SDS molecules removed from the visualization
(same simulation as Fig. 2) we see a significant reduction of the water adlayers near the SNWT. To quantify the effect, we calculated a normalized radial density distribution function for the water molecules:

$$P_w(r) = \frac{1}{\rho_w} \frac{\langle n(r,r+dr) \rangle}{2\pi dr L_z} \quad (3)$$

where $\langle n(r,r+dr) \rangle$ is the number of water molecules with center of mass between $r$ and $r + dr$ averaged over all the configurations (i.e., between steps 2-18 × 10⁶), $r$ is the cylindrical distance from the SWNT axis, $L_z$ is the length of the simulation box parallel to the SWNT, and $\rho_w$ is the density of water.

<figure><img src="image_5.png" /><figcaption>**Figure 4.** Exclusion of water molecules from the SWNT by the SDS adlayer at $T = 300$ K. (a) Simulation performed in absence of SDS. (b) Simulation performed with SDS molecules (but removed from the visualization, same simulation as Fig. 2). (c) Normalized radial density distribution function for the water molecules $P_w(r)$ around a SWNT collected from the 16-18 ns interval at $T = 300$ K (Eq. 3). The full line is the average of five runs performed under different initial conditions; dashed lines show minimum and maximum values.</figcaption></figure>

**Figure 4c** shows the results for radial density distribution function for the water molecules $P_w(r)$ at $T = 300$ K (the results for 350 K are qualitatively similar) for simulations in presence of a SWNT with and without SDS molecules present. In absence of SDS molecules there are two marked water adlayers at $r \approx 7$ and $9.5$ Å. The addition of SDS molecules shields the SWNT from water, significantly reducing the water density in the $r \lesssim 11.5$ Å region. The average $P_w(r)$ is consistent for different time intervals; variability at different time intervals is similar, and there is little correlation between minimum and maximum values from one interval to another. Some observations:

(i) For $r \lesssim 6.5$ Å the SWNT excludes water and thus $P_w = 0$; for large $r$ we expect the water density to approach that of water, i.e., $P_w \approx 1$, as observed for $r \gtrsim 15$ Å.

(ii) In absence of the SDS, water forms a strongly structured first adlayer at $r \approx 7$ Å, followed by a smaller density peak at $r \approx 9.5$ Å, consistent with earlier simulations [22].

(iii) The formation of the SDS adlayers is effective removing water from the SWNT neighborhood until $r \approx 11.5$ Å. This likely causes significant changes in the SWNT excitation spectrum.

(iv) There is some variability of results for $P_w(r)$ for different initial conditions indicating relatively slow dynamics for the SDS adlayer.
### 3.3. Variation of the shielding efficacy with temperature

In Section 3.2 we observed the significant shielding of the SWNT by the SDS adlayers in the region $r \lesssim 11.5$ Å. Integrating the radial density distribution function $P_w(r)$ indicates a ca. 70% reduction in the number of water molecules near the nanotube in this region where the effect of electrostatic interactions with an exciton is likely most significant. This exclusion varies with temperature (not shown) but this change is comparable to the variations between configurations shown in Fig. 4c for averages computed in the 16-18 ns range. We seek to quantify if the temperature dependence is significant or not. For this purpose, we analyzed data in blocks of 2 ns collected along the 2-18 ns interval. Overall, each of the $P_w(r)$'s from independent blocks are similar but with variations consistent with the intervals in Fig. 4c. In order to quantify effectiveness of shielding we integrated each radial distribution relative to the one without SDS, i.e., how many water molecules are removed by the SDS in the $0 < r < 25$ Å interval. Figure 5 shows how this number of removed water molecules per unit SWNT length $\Delta N_w$ varies during the 2-18 ns interval at $T = 300$ and 350 K. Even though $\Delta N_w$ fluctuates during the runs, it is clear that there is a significant variation of the number of excluded water molecules with temperature, with the SDS adlayer becoming (slightly) less effective as the temperature increases.

<figure><img src="image_6.png" /></figure>

**Figure 5.** Effectiveness of SDS shielding. Variation of the total number of water molecules excluded from the SWNT $\Delta N_w$ by the presence of the SDS adlayer. Each data point is calculated over an interval of 2 ns around each $\langle t \rangle$ (the datapoint for 2 ns was computed over 1 ns only). Thick lines represent the average over the five independent runs. Thin lines represent minimum and maximum values.

## 4. Summary

In this work we have presented a systematic fully atomistic molecular dynamics (MD) simulation study of a SWNT covered by an adlayer SDS molecules and immersed in water. The simulations, performed in the (N, P, T) ensemble for $18 \times 10^6$ steps of 1 fs (18 ns).

We show that the SDS adlayer is able to effectively shield the SWNT (Fig. 4), excluding ca. 70% of water molecules from the first two water adlayers ($r \lesssim 11.5$ Å) [22]. The shielding decreases with a temperature increase from 300 to 350 K (Fig. 5). This removal of water from the immediate neighborhood of the SWNT likely causes significant changes in the SWNT NIR exciton spectrum [14,15,16,24]. Although we are not able to directly show how this influences the exciton spectrum,
our results represent a possible step towards elucidating the origin of the temperature dependence of the NIR spectrum [24] and help develop the use of SWNTs as in situ thermometers.

## 5. Acknowledgements

We would like to thank Lucyna Firlej, Michael Roth, Bogdan Kuchta, Eric Anglaret, and Rosa Maria D'Ambrosio Gonçalves for useful discussions.

## Appendix: Interactions

Atomic interactions were modeled using the CHARMM force field [28]:

$$V = V_b + V_a + V_d + V_{nb}. \qquad (A1)$$

The bond stretching is described by the harmonic potential

$$V_b = \sum_{\text{bonds}} k_b (b - b_0)^2, \qquad (A2)$$

except for C-H and O-H bonds that were held rigid ($b = b_0$) [35,36]. The angle deformation potential is given by

$$V_a = \sum_{\text{angles}} k_{\theta} (\theta - \theta_0)^2 + k_{\text{UB}} (S - S_0)^2, \qquad (A3)$$

where $k_\theta$ is the angular harmonic stiffness constant, $\theta_0$ is the bond-angle equilibrium value, $k_{\text{UB}}$ is the Urey-Bradley constant and $S_0$ is the equilibrium distance between the 1-3 pairs (H-O-H angles in water were kept fixed). The four-body dihedral torsion contribution is given by

$$V_d = \sum_{\text{dihedrals}} k_{\chi} (1 + \cos(n\chi - \delta)), \qquad (A4)$$

where $k_\chi$ is the torsional stiffness, $n$ is the multiplicity factor, $\chi$ is the dihedral angle, and $\delta$ is the phase shift. Nonbonded interactions comprise two-body interactions for atom pairs either in the same or different molecule and adatom-substrate pair interactions [35,36] and are only applied to atom pairs separated by at least three bonds, with 1-4 interactions modified by a scaling factor of 0.5 [37]:

$$V_{nb} = \sum_{i,j'} \frac{q_i q_{j'}}{4\pi \epsilon r_{ij}} + \sum_{i,j'} \epsilon_{ij} \left[ \left( \frac{r_{min,ij}}{r_{ij}} \right)^{12} - 2 \left( \frac{r_{min,ij}}{r_{ij}} \right)^{6} \right], \qquad (A5)$$

where $q_i$ are the partial atomic charges, $r_{ij}$ is the interatom distance, $\epsilon$ is the dielectric constant, $\epsilon_{ij}$ is the Lennard-Jones potential depth and $r_{min,ij}$ is the distance of the Lennard-Jones minimum. Both $\epsilon_{ij}$ and $r_{min,ij}$ are obtained from the Lorentz-Berthelot combination rules [28]:

$$\epsilon_{ij} = \sqrt{\epsilon_i \epsilon_j}, \qquad r_{min,ij} = \frac{r_{min,i} + r_{min,j}}{2}. \qquad (A6)$$
Partial charges, bond lengths, angles and dihedrals were obtained from *ab initio* density functional theory calculations and are similar to those reported in the literature [29,39,40,38]. **Tables A1-A4** gather the interaction parameters used in our simulations.

<table><caption>**Table A1.** Interaction parameters: bonds [Eq. (A2)]. Atom types are CA: aromatic C in SWNT; CT2: backbone C, CT3: end C, HB: H; OS, OSC: O, and S: sulfur in SDS; OT, HT: O and H in water.</caption><thead><tr><th>Bonds</th><th>b<sub>θ</sub> [Å]</th><th>k<sub>b</sub> [kcal/(mol Å<sup>2</sup>)]</th></tr></thead><tbody><tr><td>CA-CA</td><td>1.420</td><td>305.0</td></tr><tr><td>CT2-CT2</td><td>1.530</td><td>222.5</td></tr><tr><td>CT2-CT3</td><td>1.528</td><td>225.4</td></tr><tr><td>CT2-HB</td><td>1.080</td><td>330.0</td></tr><tr><td>CT2-OSC</td><td>1.420</td><td>600.0</td></tr><tr><td>OSC-S</td><td>1.580</td><td>600.0</td></tr><tr><td>OS-S</td><td>1.460</td><td>900.0</td></tr><tr><td>OT-HT</td><td>1.0</td><td>450.0</td></tr><tr><td>HT-HT</td><td>1.5</td><td>0.0</td></tr></tbody></table>

<table><caption>**Table A2.** Interaction parameters: angles and Urey-Bradley [Eq. (A3)]. See **Table A1** for atom types.</caption><thead><tr><th>Angles</th><th>θ<sub>θ</sub> [°]</th><th>k<sub>θ</sub> [kcal/(mol rad<sup>2</sup>)]</th><th>S<sub>θ</sub> [Å]</th><th>k<sub>UB</sub> [kcal/(mol Å<sup>2</sup>)]</th></tr></thead><tbody><tr><td>CA-CA-CA</td><td>40.0</td><td>120.0</td><td>2.416</td><td>35.0</td></tr><tr><td>HT-OT-HT</td><td>55.0</td><td>104.5</td><td></td><td></td></tr><tr><td>CT2-CT2-CT2</td><td>58.4</td><td>113.6</td><td>2.561</td><td>11.2</td></tr><tr><td>CT3-CT2-CT2</td><td>58.0</td><td>115.0</td><td>2.561</td><td>8.0</td></tr><tr><td>CT2-CT2-HB</td><td>35.0</td><td>111.0</td><td></td><td></td></tr><tr><td>CT2-CT3-HB</td><td>35.0</td><td>111.0</td><td></td><td></td></tr><tr><td>CT3-CT2-HB</td><td>35.0</td><td>111.0</td><td></td><td></td></tr><tr><td>HB-CT2-HB</td><td>36.0</td><td>115.0</td><td></td><td></td></tr><tr><td>HB-CT3-HB</td><td>36.0</td><td>115.0</td><td></td><td></td></tr><tr><td>OSC-CT2-HB</td><td>50.0</td><td>118.0</td><td></td><td></td></tr><tr><td>CT2-CT2-OSC</td><td>124.3</td><td>109.5</td><td></td><td></td></tr><tr><td>CT2-OSC-S</td><td>124.3</td><td>112.6</td><td></td><td></td></tr><tr><td>OSC-S-OS</td><td>102.0</td><td>102.6</td><td></td><td></td></tr></tbody></table>

<table><caption>**Table A3.** Interaction parameters: dihedrals [Eq. (A4)]. See **Table A1** for atom types.</caption><thead><tr><th>Dihedrals</th><th>n</th><th>δ [°]</th><th>k<sub>χ</sub> [kcal/mol]</th></tr></thead><tbody><tr><td>CA-CA-CA-CA</td><td>2</td><td>180.0</td><td>3.10</td></tr><tr><td>CT2-CT2-CT2-CT2</td><td>1</td><td>0.0</td><td>0.15</td></tr><tr><td>CT3-CT2-CT2-CT2</td><td>1</td><td>0.0</td><td>0.15</td></tr><tr><td>X-CT2-CT2-X</td><td>3</td><td>0.0</td><td>0.20</td></tr><tr><td>X-CT2-CT3-X</td><td>3</td><td>0.0</td><td>0.16</td></tr><tr><td>X-CT2-OS-X</td><td>3</td><td>0.0</td><td>-0.10</td></tr><tr><td>X-CT3-CT3-X</td><td>3</td><td>0.0</td><td>0.16</td></tr><tr><td>X-CT2-OSC-S</td><td>3</td><td>0.0</td><td>-0.10</td></tr><tr><td>CT2-OSC-S-OS</td><td>1</td><td>0.0</td><td>-0.15</td></tr></tbody></table>

<table><caption>**Table A4.** Interaction parameters: non-bonded terms [Eqs. (A5,A6)]. Parentheses in the non-bonded terms denote 1-4 interaction. See **Table A1** for atom types, and SOD: Na⁺.</caption><thead><tr><th>Non-Bonded</th><th>q [esu]</th><th>ε [kcal/mol]</th><th>r<sub>min</sub>/2 [Å]</th></tr></thead><tbody><tr><td>CA</td><td>0.000</td><td>0.070</td><td>1.992</td></tr><tr><td>HT</td><td>0.417</td><td>0.046</td><td>0.225</td></tr><tr><td>OT</td><td>-0.834</td><td>0.152</td><td>1.768</td></tr></tbody></table>
<table><tr><td>CT2</td><td>-0.180</td><td>0.055</td><td>2.175</td></tr><tr><td>CT3</td><td>-0.270</td><td>0.080</td><td>2.060</td></tr><tr><td>HB</td><td>0.090</td><td>0.022</td><td>1.320</td></tr><tr><td>OSC</td><td>-0.459</td><td>0.170</td><td>1.684</td></tr><tr><td>OS</td><td>-0.654</td><td>0.200</td><td>1.768</td></tr><tr><td>SOD</td><td>1.000</td><td>0.047</td><td>1.364</td></tr><tr><td>S</td><td>1.284</td><td>0.450</td><td>2.000</td></tr></table>

# 6. Declarations

## Ethical Approval

No animals or human participants were involved in this research.

## Funding

This work was funded in part by the National Science Foundation Grant No. IIP-2044726 and a University of Missouri MizzouForward Undergraduate Research Training Grant.

## Availability of Data and Materials

All simulation models and parameters are provided within the manuscript. The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

# References

1. Iijima S (1991) Helical Microtubules of Graphitic Carbon. Nature 354:56–58.
https://doi.org/10.1038/354056a0

2. Iijima S, Ichihashi T (1993) Single-shell carbon nanotubes of 1-nm diameter. Nature 363:603-605.
https://doi.org/10.1038/363603a0

3. Odom TW, Huang JL, Kim P, Lieber CM (1998) Atomic structure and electronic properties of single-walled carbon nanotubes. Nature 391:62–64. https://doi.org/10.1038/34145

4. Ajayan PM (1999) Nanotubes from carbon. Chem Rev 99(7):1787–1800.
https://doi.org/10.1021/cr970102g

5. Jain A, Homayoun A, Bannister CW, Yum K (2015) Single-Walled Carbon Nanotubes as near- Infrared Optical Biosensors for Life Sciences and Biomedicine. J Biotech 10(3):447-459.
https://doi.org/10.1002/biot.201400168

6. Schroeder V, Savagatrup S, He M, Lin S, Swager TM (2019) Swager, T. M. Carbon Nanotube Chemical Sensors. Chem Rev 119(1):599–663. https://doi.org/10.1021/acs.chemrev.8b00340

7. Irina V. Zaporotskova, Natalia P. Boroznina, Yuri N. Parkhomenko, Lev V. Kozhitov (2016) Carbon Nanotubes: Sensor Properties. A Review. Mod Electron Mater 2(4):95–105.
https://doi.org/10.1016/j.moem.2017.02.002

8. Welsher K, Sherlock SP, Dai H (2011) Deep-tissue anatomical imaging of mice using carbon nanotube fluorophores in the second near- infrared window. Proc Natl Acad Sci USA 108:8943–8948.
https://doi.org/10.1073/pnas.1014501108

9. Tans SJ, Devoret MH, Dai H, Thess A et al (1997) Individual single-wall carbon nanotubes as quantum wires. Nature 386:474–477. https://doi.org/10.1038/386474a0

10. Bachilo SM, Strano MS, Kittrell C, Hauge RH, Smalley RE, Weisman RB (2002) Structure- Assigned Optical Spectra of Single-Walled Carbon Nanotubes. Science 298(5602):2361–2366.
https://doi.org/10.1126/science.1078727
11. O'Connell MJ, Bachilo SM, Huffman CB et al (2002) Band gap fluorescence from individual single-walled carbon nanotubes. Science 297:593-596. https://doi.org/10.1126/science.1072631

12. Kataura H, Kumazawa Y, Maniwa Y, Umezu I, Suzuki S, Ohtsuka Y, Achiba Y (1999) Optical Properties of Single-Wall Carbon Nanotubes. Synth Met 103(1):2555-2558. https://doi.org/10.1016/S0379-6779(98)00278-1

13. Monea BF, Ionete EI, Spiridon SI, Ion-Ebrasu D, Petre E (2019) Carbon Nanotubes and Carbon Nanotube Structures Used for Temperature Measurement. Sensors 19(11):2464. https://doi.org/10.3390/s19112464

14. Wang F, Dukovic G, Brus LE, Heinz TF (2005) The optical resonances in carbon nanotubes arise from excitons. Science 308:838-841. https://doi.org/10.1126/science.1110265

15. Davoody, AH, Karimi F, Arnold MS, Knezevic I (2016) Theory of Exciton Energy Transfer in Carbon Nanotube Composites. J Phys Chem C 120(30):16354-16366.
https://doi.org/10.1021%2Facsjpcc.6b04050

16. Simpson JR, Roslyak O, Duque JG, Hároz EH, Crochet JJ, Telg H, Piryatinski A, Walker ARH, Doorn SK (2018) Resonance Raman Signature of Intertube Excitons in Compositionally- Defined Carbon Nanotube Bundles. Nat Commun 9(1):637. https://doi.org/10.1038/s41467-018-03057-7

17. Xu J, Mueller R, Hazelbaker E et al (2017) Strongly Bound Sodium Dodecyl Sulfate Surrounding Single-Wall Carbon Nanotubes. Langmuir 33(20):5006-5014. https://doi.org/10.1021/acs.langmuir.7b00758

18. Silvera-Batista CA, Wang RK, Weinberg P, Ziegler KJ (2010) Solvatochromic Shifts of Single-Walled Carbon Nanotubes in Nonpolar Microenvironments. Phys Chem Chem Phys 12(26):6990-6998.
http://dx.doi.org/10.1039/b927053a

19. Chiashi S, Watanabe S, Hanashima T, Homma Y (2008) Influence of Gas Adsorption on Optical Transition Energies of Single-Walled Carbon Nanotubes. Nano Lett 8(10):3097-3101.
https://doi.org/10.1021/nl801074j

20. Kharisov BI, Kharissova OV, Dimas AV (2016) The Dispersion, Solubilization and Stabilization in "Solution" of Single-Walled Carbon Nanotubes. RSC Adv 6(73):68760-68787.
http://dx.doi.org/10.1039/C6RA13187E

21. Fujigaya T, Nakashima N (2015) Non-Covalent Polymer Wrapping of Carbon Nanotubes and the Role of Wrapped Polymers as Functional Dispersants. Sci Technol Adv Mater 16 (2):024802.
https://doi.org/10.1088/1468-6996/16/2/024802

22. Homma Y, Chiashi S, Yamamoto T, Kono K, Matsumoto D, Shitaba J, Sato S (2013) Photoluminescence Measurements and Molecular Dynamics Simulations of Water Adsorption on the Hydrophobic Surface of a Carbon Nanotube in Water Vapor. Phys Rev Lett 110(15):157402.
https://doi.org/10.1103/PhysRevLett.110.157402

23. Saito Y, Tanaka Y, Yamaguchi G, Kato T, Konabe S, Chiashi S, Homma Y (2021) Temperature Dependence of Photoluminescence Spectra from a Suspended Single-Walled Carbon Nanotube with Water Adsorption Layer. J Appl Phys 129(1):014301. https://doi.org/10.1063/5.0031611

24. D'Ambrosio RM, Nanomatériaux G (2021) à base de nanotubes de carbone monofeuillets en suspensions aqueuses: étude des perspectives de développement de capteurs thermiques et de microgels hybrides photo-actuateurs, Dissertation, Université de Montpellier, France.

25. Wołowicz, A, Staszak K (2020) Study of Surface Properties of Aqueous Solutions of Sodium Dodecyl Sulfate in the Presence of Hydrochloric Acid and Heavy Metal Ions. J Mol Liq 299:112170.
https://doi.org/10.1016/j.molliq.2019.112170

26. Cai L, Lv W, Zhu H, Xu Q (2016) Molecular Dynamics Simulation on Adsorption of Pyrene- Polyethylene onto Ultrathin Single-Walled Carbon Nanotube. Physica E Low Dimens Syst Nanostruct 81:226-234.
http://dx.doi.org/10.1016/j.physe.2016.03.021

27. Kalé K, Skeel R, Bhandarkar M, Brunner R, Gursoy A, Krawetz N, Phillips J, Shinozaki A, Varadarajan K, Schulten K (1999) NAMD2: Greater Scalability for Parallel Molecular Dynamics. J Comput Phys 151:283-312. https://doi.org/10.1006/jcph.1999.6201

28. MacKerell AD, Bashford D, Bellott M et al (1998) All-Atom Empirical Potential for Molecular Modeling and Dynamics Studies of Proteins. J Phys Chem B 102:3586-3616. https://doi.org/10.1021/jp973084f

29. Tummala NR, Striolo A (2009) SDS Surfactants on Carbon Nanotubes: Aggregate Morphology. ACS Nano 3:595-602. https://doi.org/10.1021/nn8007756
30. Yurekli K, Mitchell CA, Krishnamoorti R (2004) Small-Angle Neutron Scattering from Surfactant-Assisted Aqueous Dispersions of Carbon Nanotubes. J Am Chem Soc 126(32):9902–9903.
https://doi.org/10.1021/ja047451u

31. Rajabpour A, Akizi FY, Heyhat MM, Gordiz K (2013) Molecular dynamics simulation of the specific heat capacity of water-Cu nanofluids. Int Nano Lett 3:58. http://dx.doi.org/10.1186/2228-5326-3-58

32. Fine R, Millero FJ (1973) Compressibility of water as a function of temperature and pressure. J Chem Phys 59(10):5529-5536. http://dx.doi.org/10.1063/1.1679903

33. Millero FJ, Curry RW, Drost-Hansen W (1969) Isothermal Compressibility of Water at Various Temperatures. J. Chem and Eng. Data 14(4):422-425.

34. Wagner W, Pruss A (2002) The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use. J Phys Chem Ref Data 31(2):387-535.
http://dx.doi.org/10.1063/1.1461829

35. Roth MW, Firlej L, Kuchta B, Connolly MJ, Maldonado E, Wexler C (2016) Simulation and Characterization of Tetracosane on Graphite: Molecular Dynamics Beyond the Monolayer. J Phys Chem C 120:984-994. https://doi.org/10.1021/acs.jpcc.5b09677

36. Valleroy Z, dos Santos G, Lombardi T, Wexler C (2020) Adsorption of Natural Gas Mixtures of Methane, Ethane, and Propane in Nanoporous Carbon: Fully Atomistic Numerical Studies, Langmuir 36(14):3690-3702. https://doi.org/10.1021/acs.langmuir.9b03962

37. Lombardi T, Schaeperkoetter JC, Albesa A, Wexler C (2011) Adsorption-Induced Expansion of Graphene Oxide Frameworks with Covalently Bonded Benzene-1,4-diboronic Acid: Numerical Studies. J Mol Model 17:811-816. https://doi.org/10.1021/acsomega.2c00151

38. Ríos-López M, Mendez-Bermúdez JG, Domínguez H (2018) New Force Field Parameters for the Sodium Dodecyl Sulfate and Alpha Olefin Sulfonate Anionic Surfactants. J Phys Chem B 122:4558–4565.
https://doi.org/10.1021/acs.jpcb.8b01452

39. Tummala NR, Striolo A (2008) Role of Counterion Condensation in the Self-Assembly of SDS Surfactants at the Water-Graphite Interface. J Phys Chem B 112:1987-2000. https://doi.org/10.1021/jp077678m

40. Chun BJ, Choi JI, Jang SS (2015) Molecular dynamics simulation study of sodium dodecyl sulfate micelle: Water penetration and sodium dodecyl sulfate dissociation, Colloids and Surfaces A: Physicochem. Eng. Aspects 474:36–43. https://doi.org/10.1016/j.colsurfa.2015.03.002